Chemistry Ch. 5

Front 1

Phase

Back 1

Any part of a system that is homogeneous, meaning that the physical and chemical properties of the system are constant.

Front 2

How does a phase change occur?

Back 2

-May result when the energy of each molecule is increased or decreased
-When space around each molecule is reduced or enlarged.
-These changes are accomplished via heat or or work.

Front 3

Heat Capacity (C)

Back 3

-The measure of the energy change needed to change the temperature of a substance
-A process of energy TRANSFER

Front 4

What are the two heat capacities for any substance?

Back 4

1. Constant volume heat capacity
-since the volume of the system is held constant, no PV work is done, all energy change is in the form of heat.
-NONE of the energy going into the system can escape as work done by the system.

2. Constant Pressure Heat Capacity
-when pressure is held constant and the volume of the substance is allowed to expand, some of the energy can leave the system as PV work done on the surroundings
-at constant pressure, a substance can absorb energy with less change in temperature by expelling some of the energy to the surroundings as work.

Cp > Cv

Front 5

Equation for the heat capacity of a system

Back 5

q = Cdelta(T)
q = heat
C = heat capacity
T = temperature

Front 6

Specific heat capacity

Back 6

-The heat capacity per unit mass.

q = mcdelta(T)

m = mass
c = specific heat
T = temperature
q = heat

Front 7

The specific heat of water

Back 7

c(water) = 1 cal/gram X 1 degree C

Front 8

Calorimeter

Back 8

-A device which measures energy change.
-There are both constant pressure and constant volume calorimeters

Front 9

Coffee Cup Calorimeter

Back 9

-A constant pressure calorimeter because it measures energy change at atmospheric pressure.
-2 coffee cups are used to insulate the solution
-used to measure heats of reaction
-cannot contain expanding gases
-use q = mcdeltaT, at constant pressure q = deltaH so we can find the heat of reaction

Front 10

Bomb calorimeter

Back 10

-measures energy change at constant volume
-tells us the INTERNAL energy change of the reaction (At constant volume q = deltaU
-use q = CdeltaT to find the heat of reaction and thus the internal energy change.

Front 11

Normal melting point and Normal boiling point

Back 11

-The point in a phase change from solid to liquid. The heat capacity at this point is infinite.
-constant pressure of 1 atm
-since pressure is constant, heat equals enthalpy change (q = deltaH)

Front 12

Heat of fusion

Back 12

-the enthalpy change associated with melting.
-since pressure is constant, q = deltaH

Front 13

Heat of vaporization

Back 13

-the enthalpy change associated with boiling.
-since pressure is constant, q = deltaH

Front 14

Evaporation

Back 14

-Occurs when the partial pressure above a liquid is less than the liquid's vapor pressure, but the atmospheric pressure is greater than the vapor pressure.
-Under these conditions, the liquid evaporates rather than boils.

Front 15

What governs phase changes at constant pressure?

Back 15

-Entropy and enthalpy are both positive for processes of melting and vaporizing, and both negative for processes of freezing and condensing.
-Therefore, looking at the Gibbs Free Energy equation temperature governs the direction the reaction will move. Governs phase changes at constnat pressure.

Front 16

Phase diagram

Back 16

-indicates the phases of a substance at different pressures and temperatures.
-the lines indicate the temperatures and pressures at which the phases are in equilibrium with each other.

Front 17

Triple point

Back 17

-the point on a phase diagram at which all three phases can exist in equilibrium

Front 18

Critical temperature

Back 18

-The temperature above which a substance cannot be liquified regardless of the pressure applied.

Front 19

Critical pressure

Back 19

-The pressure required to produce liquidifaction while the substance is at critical temperature

Front 20

Critical point

Back 20

-the critical temperature and critical pressure together make up the critical point on a phase diagram
-fluid beyond the critical point has characteristics of both gas and liquid and is called a supercritical fluid

Front 21

Colligative properties

Back 21

-properties in chemistry that depend solely on the number of particles, irrespective of the type of particle

Front 22

The 4 colligative properties of solutions

Back 22

1. vapor pressure
2. boiling point
3. freezing point
4. osmotic pressure

Front 23

Equation for boiling point elevation due to the addition of a nonvolatile solute

Back 23

deltaT = K(b)mi

kb = a specific constant of the substance being boiled
m = molality of the solution
i = van't Hoff factor. number of particles into which a single solute particle will dissociate when added to solution
-addition of a nonvolatile solute decreases vapor pressure and increases boiling point.
-this cannot be applied to volatile solutes (which decrease the boiling point by increasing vapor pressure).

Front 24

van't Hoff factor

Back 24

-the number of particles into which a single solute particle will dissociate when added to solution.
-used in boiling point elevation eq.

Front 25

Freezing point depression

Back 25

deltaT = k(f)mi

kf = constant specific for substance being frozen
m = molality
i = van't Hoff factor

-Impurities interrupt the crystal lattice and lower the freezing point of a liquid.
-At a certain point, the solvent will become the impurity preventing the solute from freezing and the freezing point will rise as more is added.

Front 26

van't Hoff factor

Back 26

-the number of particles into which a single solute particle will dissociate when added to solution.
-used in boiling point elevation eq.

Front 27

Freezing point depression

Back 27

deltaT = k(f)mi

kf = constant specific for substance being frozen
m = molality
i = van't Hoff factor

-Impurities interrupt the crystal lattice and lower the freezing point of a liquid.
-At a certain point, the solvent will become the impurity preventing the solute from freezing and the freezing point will rise as more is added.

Front 28

Osmotic pressure

Back 28

-a measure of the tendency of water to move into a solution via osmosis.

Front 29

Equation for osmotic pressure

Back 29

osmotic pressure = iMRT

M = molarity of the solution
i = van't Hoff factor
T = temperature