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71 Cards in this Set

  • Front
  • Back
  • 3rd side (hint)

Calculate the average molar bond enthalpy of the carbon-hydrogen bond in a CH4 molecule?

Write equation: C(s) + 2H2(g) = CH4 (g)




(Pss you gotta use the hess law here)


Average molar bond enthalpy of the carbon-hydrogen bond in a CH4 molecule = (+716.7 + (4 x 218) - (- 74.6) ) / 4 = + 1663.3 / 4 =+416 KJ/mol


Bromination of isobutane is a two-step reaction, as shown below. Using the table of bond dissociation energies below, calculate the enthalpy of each step and the enthalpy of the overall reaction.


Energy is absorbed when a bond breaks, so the bond dissociation enthalpy is positive. When the bond is formed, an amount of energy equal to the bond dissociation enthalpy is released; therefore, the bond formation enthalpy has the same numeric value as the dissociation enthalpy, but it is negative.


The reaction enthalpy can be estimated by subtracting the bond energies for bonds formed from the total bond energies for bonds broken.


ΔHrxn = Σ(ΔH bonds broken) – Σ(ΔH bonds formed)


Step 1: C–H bond broken and H–Br bond formed ΔH = 400 kJ/mol – 366 kJ/mol = 34 kJ/mol


Step 2: Br–Br bond broken and C–Br bond formed ΔH = 194 kJ/mol – 292 kJ/mol = –98 kJ/mol Overall reaction: ΔH = (400 kJ/mol 194 kJ/mol) – (366 kJ/mol 292 kJ/mol) = –64 kJ/mol



Also, we can apply Hess\'s law that states that the enthalpy change of an overall process is the sum of the enthalpy changes of its individual steps. ΔHrxn = ΔHstep1 ΔHstep2 = 34 kJ/mol (–98 kJ/mol) = –64 kJ/mol

Rate of vaporization

For a given liquid, the rate of vaporization increases with increasing temperature and surface area.


C > B because of temperature B > A because of surface area Thus, the ranking is C > B > A. Keep in mind that the rate of vaporization is not the same thing as vapor pressure. Vapor pressure (force per unit area) is unaffected by surface area.


Vapor pressure describes the pressure of the vapor phase in equilibrium with the liquid phase of a substance. Here are some things to consider.


• Pressure is force per unit area.


• If there is net evaporation or condensation, then the system is not at equilibrium.


• Different liquids have different vapor pressures.


Heat of vaporization problem

Find specific heat of gas problem

Final temp question #9

System and work

A system that does work on the surroundings has a negative value for work, w.


Problem #11 how much work must be done on a system to decrease volume from 16L to 9L at constant pressure 4atm.

Got negative... Need to do change in initial minus final

Calculate work from the following system if 17.3g of NaN3 reacts completely at 1atm and 22'C

Find mol of NaN3 then use eq to find N2 mol... Then find volume by PV=nRT.. Then plug here

Which of the following substances have a standard heat of formation (ΔHf°) of zero?

O2(g) at 25.0 °C and 1 atm




The standard heat of formation is zero for an element in its most stable form at 298 K and 1 atm.

Problem #25

Problem #21 Calories per gram

Problem #13

Part 1

2 part

Problem #14

In a constant-pressure calorimeter, 70.0 mL of 0.320 M Ba(OH)2 was added to 70.0 mL of 0.640 M HCl. The reaction caused the temperature of the solution to rise from 23.19 °C to 27.55 °C. If the solution has the same density and specific heat as water (1.00 g/mL and 4.184 J/g·K, respectively), what is ΔH for this reaction (per mole of H2O produced)? Assume that the total volume is the sum of the individual volumes.

..

The amount of heat released by the reaction is equal to the amount of heat absorbed by the solution. Once you\'ve found the heat released, divide it by the number of moles of H2O produced. Finally, pay attention to the sign of ΔH. Since the temperature increased, we know the reaction was exothermic.

Energy and energy transfer
Energy is: a property of objects, transferable among them via fundamental interactions, which can be converted in form but not created or destroyed.Work and heat : two different ways that an objectcan exchange energy with other objects.
Work and heat
Work is a force acting over a distance.

Work = (force) ⋅ (distance)


w = F ⋅ d (recall F = ma)


Heat is the flow of energy caused by a differencein the temperature.

Classification ofEnergy
Kinetic energy:energy of motion or energythat is being transferred.



Potential energy:energy that is stored in an object, orenergy associated with the composition andposition of the object.

iclicker question: Classification of Energy

1: Thermal energy:energy associated with temperature.Is thermal energy a form of kinetic or potentialenergy?

A) Kinetic energy


B) Potential energy


Answer in Hint




2: Chemical energy:energy stored in the structure of a compound:the attachment between atoms, the atoms’ positionsrelative to each other in the molecule, or themolecules’ relative positions in the structure


Is chemical energy a form of kinetic or potentialenergy?


A)Kinetic energy


B)Potential energy




3: Electrical energy:energy associated with the flow of electricalcharge.


Is electrical energy a form of kinetic or potentialenergy?


A) Kinetic energy


B) Potential energy

1: A)Thermal energy is a form of kinetic energy(molecular motion).

2:B) Chemical energy is a form of potentialenergy (associated with positions ofelectrons and nuclei).


3:A)Electrical energy is a form of kineticenergy

iclicker question: Classification of Energy

1:Light or radiant energy:energy associated with energy transitions inan atom.


Is light energy a form of kinetic or potential energy?


A) Kinetic energyB) Potential energy


2:Nuclear energy:energy stored in the nucleus of an atom.


Is nuclear energy a form of kinetic or potentialenergy?


A) Kinetic energyB) Potential energy

1:A)Light energy is a form of kinetic energy


2:B) Nuclear energy is a form of potentialenergy

Some Forms of Energy

Electrical– Kinetic energy associated with the flow of electrical charge

Heat or thermal energy– Kinetic energy associated with molecular motion


Light or radiant energy– Kinetic energy associated with energy transitions in anatomNuclear– Potential energy stored in the nucleus of atomsChemical– Potential energy stored in the structure of the atoms, theattachment between atoms, the atoms’ positions relative toeach other in the molecule, or the molecules’ relativepositions in the structure

Units of Energy
The amount of kinetic energy anobject has is directly proportionalto its mass and velocity. KE = ½mv2

1 joule of energy is the amountof energy needed to move a 1 kgmass at a speed of 1 J= 1 kg*m2/s2= 1 N*m


A calorie (cal) is the amount of energy needed toraise the temperature of one gram of water 1 °C.


– kcal = energy needed to raise 1000 g of water 1 °C


– food Calories = kcals

System and Surroundings
We define the system as the material or processwithin which we are studying the energychanges.

We define the surroundings as everything elsewith which the system can exchange energy.


ΔEnergysystem = - ΔEnergysurroundings

Internal Energy
  The internal energy is the sum of the kinetic and
potential energies of all of the particles that compose
the system.     The change in the internal energy of a system only
depends on the amount of energy in the system at
the beginning a...
The internal energy is the sum of the kinetic andpotential energies of all of the particles that composethe system.

The change in the internal energy of a system onlydepends on the amount of energy in the system atthe beginning and end. Energy is a state function.


Hint



Energy Flow in a Chemical Reaction
The total amount of internal energyin 1 mole of C(s) and 1 mole ofO2(g) is greater than the internalenergy in 1 mole of CO2(g).

At the same temperature andpressure.


In the reaction


C(s) + O2(g) → CO2(g),


there will be net release of energyfrom the reaction into thesurroundings.


−ΔEreaction = ΔEsurroundings




In the reaction


CO2(g) → C(s) + O2(g),


there will be absorption of energyfrom the surroundings into thereaction.


ΔEreaction = − ΔEsurroundings

Energy Flow

  When energy flows out of a
system, it must all flow into
the surroundings.
When energy flows out of a
system, ΔEsystem is negative.
When energy flows into the
surroundings, ΔEsurroundings is
positive. Therefore,
 ─ ΔEsystem= ΔEsu...
When energy flows out of asystem, it must all flow intothe surroundings.When energy flows out of asystem, ΔEsystem is negative.When energy flows into thesurroundings, ΔEsurroundings ispositive.

Therefore,


─ ΔEsystem= ΔEsurroundings


Hint

When energy flows into asystem, it must all comefrom the surroundings.When energy flows into asystem, ΔEsystem is positive.When energy flows out ofthe surroundings,ΔEsurroundings is negative.Therefore,ΔEsystem= ─ ΔEsurroundings

Heat and Work

On a smooth table, most of the kinetic energy istransferred from the white ball to the purple ball,with a small amount lost through friction.


Energy change for the white ball is as follows:


ΔE = KEfinal − KEinitial = 0.0 J − 5.0 J = −5.0 J


Kinetic energy transferred to purple ball: w = −4.5 J.


Kinetic energy lost as heat: q = −0.5 J.


q + w = (−0.5 J) + (−4.5 J) = −5.0 J = ΔE


Rougher table:


Energy change for the white ball is as follows:


ΔE = KEfinal − KEinitial = 0.0 J − 5.0 J = −5.0 J


Kinetic energy transferred to purple ball: w = −3.0 J.


Kinetic energy lost as heat:


q = −2.0 J.q + w = (−2.0 J) + (−3.0 J) = −5.0 J = ΔE



ΔE of the white ball is the same forboth cases, but q and w are not.


On the rougher table, the heat loss, q, is greater.q is a more negative number.


But on the rougher table, less kinetic energy istransferred to the purple ball, so the work done by thewhite ball, w, is less.


w is a less negative number.


ΔE is a state function and depends only on thevelocity of the white ball before and after the collision.


In both cases it started with 5.0 kJ of kinetic energy andended with 0.0 kJ because it stopped.q + w is the same for both tables, even though the values ofq and w are different.

Heat Exchange
Heat is the exchange of thermal energy between asystem and surroundings.

Heat exchange occurs when system andsurroundings have a difference in temperature.Temperature is the measure of the thermal energywithin a sample of matter.


Heat flows from matter with high temperature tomatter with low temperature until both objects reachthe same temperature: thermal equilibrium


Heat Capacity


When a system absorbs heat, its temperatureincreases.


The increase in temperature is directly proportionalto the amount of heat absorbed: q ∝ ΔT


The proportionality constant is called the heatcapacity, C: q = C × ΔT


(change temp Tf-Ti)


Units of C: J/°C or J/K.


The larger the heat capacity of the object beingstudied, the smaller the temperature rise will be fora given amount of heat.


Factors Affecting Heat Capacity


The heat capacity of an object depends on itsamount of


matter.


The heat capacity of an object depends on the typeof material.

Heat Transfer and Final Temperature

When two objects at different temperatures areplaced in contact, heat flows from the object at thehigher temperature to the object at the lowertemperature.


Heat flows until both objects reach the same finaltemperature.


The amount of heat energy lost by the hot objectequals the amount of heat gained by the cold object.


qhot object = - qcold object



Thermal Energy Transfer



A block of metal at 55 °C is added to water
at 25 °C.
Thermal energy transfers heat from the metal to
the water.
The exact temperature change depends on: 
The mass of the metal 
The mass of water 
Specific heat capacities of the meta...

A block of metal at 55 °C is added to waterat 25 °C.Thermal energy transfers heat from the metal tothe water.The exact temperature change depends on:


The mass of the metal


The mass of water


Specific heat capacities of the metal and of water




Hint

Pressure-Volume Work

PV work is work caused by a volume changeagainst an external pressure.


Example: When gases expand, the volumeincreases against external pressure, and thesystem is doing work on the surroundings


When gases expand, ΔV is positive, but the systemis doing work on the surroundings, so wgas isnegative.


As long as the external pressure is kept constant, Workgas = External Pressure × Change in Volumegas


w = - Pext ΔV


To convert the unitsto joules use:101.3 J = 1 atm · L.


Hint

Measuring ΔE: Calorimetry at ConstantVolume

Because ΔE = q + w, we can determine ΔE bymeasuring q and w.


In practice, it is easiest to determine ΔE whenthere is no change in volume. Under theseconditions w = 0.


At constant volume:


ΔEsystem = qsystem


A bomb calorimeter is aconstant volume system:ΔEcalorimeter = qcalorimeterqcalorimeter = - qsystem


Hint



When 1.010 g of sucrose (C12H22O11) undergoes combustion in a bomb
calorimeter, the temperature rises from 24.92 °C to 28.33 °C. Find
ΔErxn for the combustion of sucrose in kJ/mol sucrose. The heat
capacity of the bomb calorimeter, dete...

When 1.010 g of sucrose (C12H22O11) undergoes combustion in a bombcalorimeter, the temperature rises from 24.92 °C to 28.33 °C. FindΔErxn for the combustion of sucrose in kJ/mol sucrose. The heatcapacity of the bomb calorimeter, determined in a separate experiment,is 4.90 kJ/°C. (You can ignore the heat capacity of the small sample ofsucrose because it is negligible compared to the heat capacity of thecalorimeter.)



Enthalpy

The enthalpy, H, of a system is the sum of theinternal energy of the system and the product ofpressure and volume.


H = E + PV


H is a state function.


The enthalpy change, ΔH, of a reaction is the heatevolved in a reaction at constant pressure:


ΔHreaction = qreaction at constant pressure


Usually ΔH and ΔE are similar in value; thedifference is largest for reactions that produce oruse large quantities of gas.


The enthalpy change in a chemical reaction is anextensive property.


The more reactants you use, the larger the enthalpychange.By convention, we calculate the enthalpy changefor the number of moles of reactants in the reactionas written.C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g) ΔH = −2044 kJ 1 mol C3H8(g) = –2044 kJ or 5 mol O2(g) = –2044 kJ


Hint

Endothermic and Exothermic Reactions
When ΔH is negative, heat isbeing released by thesystem.This is called anexothermic reaction

Chemical heat packs contain iron filings thatare oxidized in an exothermic reaction.




When ΔH is positive, heat isbeing absorbed by thesystem.This is called anendothermic reaction.


Chemical cold packs contain NH4NO3 that dissolves in waterin an endothermic process

Exothermic and Endothermic Processes iclicker
a. sweat evaporating from skin

b. water freezing in a freezer


c. wood burning in a fire


A) a: endothermic, ΔH<0 ; b: exothermic, ΔH>0 ; c: exothermic, ΔH>0




B) a: exothermic, ΔH>0 ; b: exothermic, ΔH>0 ; c: endothermic, ΔH<0




C) a: endothermic, ΔH>0 ; b: exothermic, ΔH<0 ; c: exothermic, ΔH<0




D) a: exothermic, ΔH<0 ; b: endothermic, ΔH>0 ; c: exothermic, ΔH<0

C:


a. Sweat evaporating from skin cools the skin and is thereforeendothermic, with a positive ΔH. è


a: endothermic, ΔH>0


b. Water freezing in a freezer releases heat and is thereforeexothermic, with a negative ΔH. è


b: exothermic, ΔH<0


c. Wood burning in a fire releases heat and is therefore exothermic,with a negative ΔH. è


c: exothermic, ΔH<0



Molecular View of Exo and Endothermic Reactions
For an exothermic reaction,the surrounding’stemperature rises due to arelease of thermal energy bythe reaction This extra thermal energy comes from the conversionof some of the chemical potential energy in thereactants into kinetic energy in the form of heat.

During the course of a reaction, existing bonds arebroken and new bonds are made.


The products of the reaction have less chemicalpotential energy than the reactants.


The difference in energy is released as heat.




In an endothermic reaction,the surrounding’s temperaturedrops due to absorption ofsome of its thermal energy bythe reaction.


During the course of a reaction, existing bonds arebroken and new bonds are made.


The products of the reaction have more chemicalpotential energy than the reactants.


To acquire this extra energy, some of the thermalenergy of the surroundings is converted into chemicalpotential energy stored in the products.

Measuring ΔH Calorimetryat Constant Pressure

The calorimeter is often nested foamcups containing the solution.


qreaction = - qsolution


= -(masssolution × Cs, solution × ΔT)


ΔHreaction = qconstant pressure = qreaction


To get ΔHreaction per mol, divide by the numberof moles.


Hint

Hess's Law

1. When reaction is multiplied by a factor, ΔHrxn ismultiplied by that factor.


2. If a reaction is reversed, then the sign of ΔH ischanged.


3. If a reaction can beexpressed as a series ofsteps, then the ΔHrxn forthe overall reaction isthe sum of the heats ofreaction for each step.

Standard Conditions

The standard state is the state of a material at adefined set of conditions.


Pure gas at exactly 1 atm pressure


Pure solid or liquid in its most stable form at exactly 1 atmpressure and temperature of interest: usually 25 °CSubstance in a solution with concentration 1 M


The standard enthalpy change, ΔH°, is theenthalpy change when all reactants and productsare in their standard states.


The standard enthalpy of formation, ΔHf°, is theenthalpy change for the reaction forming 1 mole of apure compound from its constituent elements.


The elements must be in their standard states.


The ΔHf° for a pure element in its standard state = 0 kJ/mol.


Chart-given

Writing Formation Reactions:Write the Formation Reaction for CO(g)

The formation reaction is the reaction between theelements in the compound, which are C and O.


C + O → CO(g)


The elements must be in their standard state.There are several forms of solid C, but the one with ΔHf° = 0 isgraphite.Oxygen’s standard state is the diatomic gas.**


C(s, graphite) + O2(g) → CO(g)The equation must be balanced, but the coefficient ofthe product compound must be 1.**


Use whatever coefficient in front of the reactants is necessary tomake the atoms on both sides equal without changing theproduct coefficient.


C(s, graphite) + ½ O2(g) → CO(g)

Write equation for the formation of MgCO3(s) from its respective elementsin its standard states. Include the value of ΔHf°(MgCO3) = -1095.8 kJ/mol.


What is the coefficient in front of the oxygen?


A) 3 B) 1 C) 1/2 *D) 3/2*


Diatomic--need to make O2=O3 DeltaHf-stays the same

Calculating Standard Enthalpy Change for aReaction

ΔH°reaction = Σ npΔHf°(products) − Σ nrΔHf°(reactants)


Σ means sum.


np and nr are the coefficients in the chemical equation of thereaction for the reactants and products.


**In example can use Hess's Law or this equation

ΔH°rxn and Standard Enthalpies of Formation iclicker

Hint

Hint

Bond Energies

Chemical reactions involve breaking bonds inreactant molecules and making new bonds to createthe products.


The amount of energy it takes to break one mole ofa bond in a compound is called the bond energy.


In general, the more electrons two atoms share, thestronger the covalent bond. (double-triple bonds)


Because the actual bond lengthdepends on the other atoms aroundthe bond we often use the averagebond length.


Generally, bond length decreases from left to rightacross period --> Bonds get stronger across the period.


C—C (154 pm) > C—N (147 pm) > C—O (143 pm)


Generally, bond length increases down the column --> Bonds get weaker down the column.


F—F (144 pm) > Cl—Cl (198 pm) > Br—Br (228 pm)

Using Bond Energies to Calculate ΔH°rxn

Hint

Bonds formed - negative (require energy) ***

Bonds formed - negative (require energy) ***

Determining the Enthalpy Change for aReaction

Vaporization

Molecules in the liquid are constantlyin motion.


Vibrational, and limited rotationaland translational


The average kinetic energy is proportional to the temperature.


However, some molecules have more kinetic energythan the average, and others have less.


If these high energy molecules are at the surface,they may have enough energy to overcome theattractive forces.This will allow them to escape the liquid and becomea vapor.


When the high energy molecules are lost from theliquid, it lowers the average kinetic energy.


If energy is not drawn back into the liquid, itstemperature will decrease; therefore, vaporizationis an endothermic process.


Condensation is an exothermic process.


Vaporization requires input of energy to overcomethe attractions between molecules. Hint

Some molecules of the vapor will lose energythrough molecular collisions.The result will be that some of the molecules will getcaptured back into the liquid when they collide with it.Also some may stick and gather together to formdroplets of liquid, particularly on surroundingsurfaces.We call this process condensation.

Heat of Vaporization

The amount of heat energy required to vaporize
one mole of the liquid is called the heat of
vaporization, ΔHvap. Sometimes called the enthalpy of vaporization 
It is always endothermic; therefore, ΔHvap is +. 
It is somewhat temperature depe...

The amount of heat energy required to vaporizeone mole of the liquid is called the heat ofvaporization, ΔHvap. Sometimes called the enthalpy of vaporization


It is always endothermic; therefore, ΔHvap is +.


It is somewhat temperature dependent.


ΔHcondensation = −ΔHvaporization

Dynamic Equilibrium

In a closed container, once the rates ofvaporization and condensation are equal, the totalamount of vapor and liquid will not change.Evaporation and condensation are still occurring,but because they are opposite processes, there isno net gain or loss of either vapor or liquid.

Vapor Pressure

The pressure exerted by the vapor when it is indynamic equilibrium with its liquid is called the vaporpressure.


The weaker the attractive forces between themolecules, the more molecules will be in the vapor.


Therefore, the weaker the attractive forces, thehigher the vapor pressure.


The higher the vapor pressure, the more volatile the liquid.


Hint




vs. temp


Increasing the temperature increases the number ofmolecules able to escape the liquid.


The net result is that as the temperatureincreases, the vapor pressure increases.

If the volume of the chamber is increased, it willdecrease the pressure of the vapor inside thechamber.At that point, there are fewer vapor molecules in agiven volume, causing the rate of condensation toslow.Therefore, for a period of time, the rate of vaporizationwill be faster than the rate of condensation, and theamount of vapor will increase.

Vapor-Liquid Dynamic Equilibrium iclicker

What happens to the vapor pressure of a substance whenits surface area is increased at constant temperature?


A) The vapor pressure increases


B) The vapor pressure decreases


C) The vapor pressure remains the same

C

Boiling Point

When the temperature of a liquid reaches a pointwhere its vapor pressure is the same as theexternal pressure is called


boiling


temperature at which the vapor pressure equalsexternal pressure is the boiling point.


The normal boiling point is the temperature atwhich the vapor pressure of the liquid = 1 atm.


The lower the external pressure, the lower the boilingpoint of the liquid.


Everest 78


Boston 100

Clausius–Clapeyron Equation

Clausius–Clapeyron Equation:Two-Point Form

The equation below can be used with just twomeasurements of vapor pressure and temperature.However, it generally gives less precise results.


It can also be used to predict the vapor pressure ifyou know the heat of vaporization and the normalboiling point.Remember, the vapor pressure at the normal boiling point is760 torr.


Hint

Melting

Melting = Fusion


Once the temperature reaches the melting point,the molecules have sufficient energy to overcomesome of the attractions that hold them in positionand the solid melts (or fuses).


The opposite of melting is freezing.


When the high energy molecules are lost from thesolid, it lowers the average kinetic energy.If energy is not drawn back into the solid itstemperature will decrease; therefore, melting is anendothermic process, and freezing is anexothermic process.


Melting requires input of energy to overcome theattractions among molecules.


The amount of heat energy required to melt onemole of the solid is called the heat of fusion, ΔHfus.


It is somewhat temperature dependent.

Changes in State iclicker

Which process releases the greatest amount of heat?


A) The condensation of 10 g of gaseous water


B) The freezing of 10 g of liquid water


C) The boiling of 10 g of liquid water


D) The melting of 10 g of ice

A

Sublimation and Deposition

Molecules in the solid have thermalenergy that allows them to vibrate.


Surface molecules with sufficient energymay break free from the surface andbecome a gas; this process is calledsublimation.ΔHsublimation = ΔHfusion + ΔHvaporization

heating curve of solid and liquid

(a) A cylinder equipped with a piston expands against an external pressure of 1.58 atm. Ifthe initial volume is 0.485 L and the final volume is 1.245 L, how much work (in J) is done?



(b) When fuel is burned in a cylinder equipped with a piston, the volume expands from0.255 L to 1.45 L against an external pressure of 1.02 atm. In addition, 875 J is emitted asheat. What is ΔE for the burning of the fuel?

Vf-Vi * (- extP) --don't forget to convert to joules


101.33 J = 1 atm




Vf-Vi * (-extP) = -123.5


Heat emitted is -875


-123.5+-875= -998.5

(a) When 1.550 g of liquid hexane (C6H14) undergoes combustion in a bomb calorimeter,the temperature rises from 25.87°C to 38.13°C. Find ΔErxn for the reaction in kJ/molhexane. The heat capacity of the bomb calorimeter, determined in a separate experiment,is 5.73 kJ/ °C.

a: ΔE=qv (with no work)


to just get kj because trying to find in kj/mol


multiply 5.73kj/c by (38.13-25.87c) to just get kj


then use mass to find mols then divide kj/mol





Identify each process as endothermic or exothermic and indicate the sign of ΔH.(a) an ice cube melting(b) nail polish remover quickly evaporating after it is accidentally spilled on the skin(c) gasoline burning within the cylinder of an automobile engine

endo +


endo +


exo -

(a) Ammonia reacts with oxygen according to the equation:Calculate the heat (in kJ) associated with the complete reaction of 155 g of NH3

(b) What mass of butane in grams is necessary to produce 1.5 × 103 kJ of heat? Whatmass of CO2 is produced?

4nh3+5O2==>4NO+6H2O




155g/12.08 x -906kJ/1 mol


find mole


stoich w/ delta H to find kJ


=+2061.5






producing heat negative divide by delta H


-1.5x103kj/-2658kj/mol x 58 g/mol to get grams









When 50.0 mL of 0.100 M AgNO3 is combined with 50.0 mL of 0.100 M HCl in a coffeecupcalorimeter, the temperature changes from 23.40°C to 24.21°C. Calculate ΔHrxn for thereaction as written. Use 1.00 g/mL as the density of the solution and C = 4.18 J/g · °C asthe specific heat capacity.
ΔHrxn=qrxn=-qsol

qsol= mxCsxΔT


-4.18x(24.21-23.4 x(100mlx1.00g/ml)=-338.58



50ml x 1L/1000ml x 0.100mol/ 1L = 0.005


-338.58J/0.005mol = -67716



J-->kJ /1000



Write equations for the formation of (a) NaCl(s) and (b) Pb(NO3)2(s) from their respectiveelements in their standard states. Include the value of for each equation.

Na+Cl2-->NaCl


Na+1/2Cl2-->NaCl


0 + 0 -411.2 =-411.2




Pb + N2 + *3*O2 --> Pb(NO3)2


-451.9

The thermite reaction, in which powdered aluminum reacts with iron oxide, is highlyexothermic.

Use standard enthalpies of formation to find for delta H the thermite reaction


2Al+Fe2O3-->Al2O3 + 2Fe


n(delta H products) - n( delta H reactants)

Chemical hand warmers produce heat when they are removed from their airtight plasticwrappers by utilizing the oxidation of iron to form iron oxide according to the reaction

Calculate delta H for this reaction and calculate how much heat is produced from a handwarmer containing 15.0 g of iron powder.


solving for delta H rxn=-1648.4kj/mol




15g x 1 mol / 55.85gmol x -1648.4 kjmol / 4 mole**


use mass- molar mass- stoich- and then delta H



What mass of CO2 (in kg) does the combustion of a 15-gallon tank of gasoline release intothe atmosphere? Assume the gasoline is pure octane (C8H18) and that it has a density of0.70 g/mL.

write equation - balance


15gallon convert to L - convert to ml - use density to convert to g- find moles with molar mass


use stoich to find moles of CO2 -then use molar mass to find grams

. (a) Write a balanced equation for the combustion of gaseous methanol (CH3OH), and usebond energies to calculate the enthalpy of combustion of methanol in kJ/mol.

(b) Use bond energies to calculate ΔHrxn for the reaction:



Reactant first





Reactant first

Calculate the amount of heat (in kJ) required to vaporize 2.58 kg of water at its boilingpoint.




Suppose that 0.48 g of water at 25 °C condenses on the surface of a 55 g block ofaluminum that is initially at 25 °C. If the heat released during condensation goes onlytoward heating the metal, what is the final temperature (in °C) of the metal block? (Thespecific heat capacity of aluminum is 0.903 J/g·°C.)

going from liquid to gas write out equation H2O (l) --> H2O (g) 
find standard enthalpy
delta H=in kJ/mol
use 2.58kg convert to g use molar mass find moles find kJ

going from liquid to gas write out equation H2O (l) --> H2O (g)


find standard enthalpy


delta H=in kJ/mol


use 2.58kg convert to g use molar mass find moles find kJ

The vapor pressure of carbon tetrachloride was measured as a function of thetemperature, and the following results were obtained:


Determine the heat of vaporization of carbon tetrachloride

melting of ice bigger role

melting of ice bigger role