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37 Cards in this Set
- Front
- Back
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Definition: Thermochemistry |
The study of the relationships between chemistry and energy |
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Definition: Energy |
The capacity to do work |
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Definition: Work |
Force acting through a distance |
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Definition: Heat |
The flow of energy caused by a temperature difference (high to low) |
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Definition: Kinetic energy |
Energy associated with motion |
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Definition: Thermal energy |
Energy associated with temperature (a type of kinetic energy) |
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Definition: Potential energy |
Energy associated with position or composition |
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Definition: Chemical energy |
Energy associated with the relative positions of electrons and nuclei in atoms and molecules (a type of potential energy) |
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Definition: System |
The portion of the universe that is singled out for investigation |
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Definition: Surroundings |
Everything outside of the system |
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Units of energy |
joule (J) = 1kg m^2/s^2 calorie (cal), the energy it takes to raise 1g of water 1°C = 4.184 J Calorie (C) = 1000 cal kilowatt-hour (kWh) = 3.60 x 10^6 J |
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Formula for change in energy of a reaction |
ΔE = Eproducts - Ereactants ΔE is negative when the reaction gives off energy ΔE is posative when the reaction absorbs energy |
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Relationship between ΔEsys and ΔEsurr |
ΔEsys = -ΔEsurr |
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Two factors that make up change in energy |
ΔE = heat transferred + work done ΔE = q + w |
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Definition: Thermal equilibrium |
When heat transfer stops because the substances have reached the same temperature |
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Definition: Heat capacity |
Symbol: C The quantity of heat required to change the temperature of the system by 1°C |
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Formula for heat capacity |
C = q/ΔT = J/°C also know the arrangement of that, q = C x ΔT |
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Definition: Specific heat capacity |
Symbol: Cs Unit: J/g The intrinsic capacity of a substance to absorb heat. The amount of heat required to raise the temp. of 1g of the substance by 1°C |
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Definition: Molar heat capacity |
Unit: J/mol x °C The amount of heat required to raise the temp. of 1 mol of a substance by 1°C |
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Heat capacity is a _______ property Specific heat capacity and molar heat capacity are _______ properties |
extensive (depends on how much is being heated) intensive (a constant for that substance) |
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Formula for heat using specific heat capacity |
heat = mass x specific heat capacity x temp. change q = m x Cs x ΔT |
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Relationship between qsys and qsurr |
qsys = -qsurr |
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Formula for work |
w = -pressure x change in volume w = -P x ΔV convert units from atm x L to J use the conversion factor 101.3 J = 1 atm x L |
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Formula for change in heat of a reaction at constant volume |
ΔErxn = heat at constant volume ΔErxn = qv |
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Definition: Calorimetry
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A process in which we deduce the thermal energy exchanged between a reaction and the surroundings by measuring the change in temp. of the surroundings |
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Enthalpy means we are observing the system under constant _______ |
pressure
i.e. how we feel about chem class |
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Formula for enthalpy |
Symbol: H H = E + PV |
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Formula for change in enthalpy |
ΔH = heat at constant pressure ΔH = qp |
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The difference between ΔE and ΔH |
ΔE represents change in heat and work ΔH just represents change in heat |
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Definition: Exothermic reaction |
A reaction that gives off heat to its surroundings |
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Definition: Endothermic reaction |
A reaction that absorbs heat from its surroundings |
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Standard states by state of matter |
Gas: pure gas at pressure of 1 atm Liquid or Solid: pure in its most stable form at 1 atm and the temp. of interest (usually 25°C) Substance in solution: at concentration of 1M |
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Definition: Standard enthalpy change |
Symbol: ΔH° The change in enthalpy for a process when all reactants and products are in their standard states (that's what the ° means) |
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Definition: Standard enthalpy of formation / standard heat of formation |
Symbol: ΔH°f For a pure compound: The change in enthalpy when one mol of the compound forms from its constituent elements in their standard states. For a pure element in its standard state: ΔH°f = 0 |
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Definition: Decomposition |
When a compound breaks down into it's constituent elements in their standard states. Reverse the sign on ΔH°f |
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Rules for ΔHrxn in chemical equations |
1. If the equation is multiplied by a factor, multiply ΔHrxn by the factor
2. If the equation is reversed ΔHrxn changes sign 3. If an equation is the sum of a series of steps the the ΔHrxn for the overall rxn is the sum of the ΔHrxn's for each step |
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To calculate the ΔH°frxn |
Subtract the enthalpies of formation of the reactants multiplied by their stoichiometric coefficients from the enthalpies of formation of the products multiplied by their stoichiometric coefficients. ΔH°frxn = ∑npH°f(products) - ∑nrH°f(reactants) |
