AP Chemistry: Thermodynamics

thermodynamics

the study of heat and its transformations

thermochemistry

changes in heat that take place during chemical process

kinetic energy

the energy of motion

potential energy

stored energy

system

part of the universe we are studying

surroundings

the rest of the universe

1 joule (J) =

1 kg m^2/s^2

calorie

the amount of energy needed to raise the temperature of 1 g of water 1 degree C

1 calorie (cal) =

4\.184 J

1 nutritional Calorie (Cal) =

1000 cal

S°

standard entropy

G°

standard Gibbs free energy

c

specific heat capacity

H°

standard enthalpy

q

heat

Gas constant *R* (in terms of J per mol K)

8\.314 J mol^-1 K^-1

KE

kinetic energy

T

temperature

n

moles

m

mass

delta G° =

delta H° - T delta S°

calorimetry

laboratory technique used to measure the heat released or absorbed during a chemical or physical change

heat capacity

the quantity of heat needed to change the temperature 1 K

heat capacity =

q/delta T

heat capacity units

J/K

specific heat capacity (*c*)

quantity of heat needed to raise the temperature of 1 g of a substance 1 K

equation for specific heat

q=cm delta T

specific heat capacity units

J/g · K

molar heat capacity (C)

amount of heat needed to change the temperature of 1 mol of a substance by 1 K

what are two types of calorimeters

coffee-cup calorimeter and a bomb calorimeter

coffee-cup calorimeters have constant

pressure

bomb calorimeters have constant

volume

coffee-cup calorimeters are used to measure

changes in reactions that are open to the atmostphere and the specific heats of solids

describe the basic functioning of a coffee calorimeter

a known mass of a solid is heated to a certain temperature than added to a known mass of water at a known temperature in the calorimeter. the final temperature is recorded

bomb calorimeters are used to measure

energy changes in combustion reactions

describe the basic functioning of a bomb calorimeter

compressed oxygen is added to a weighed sample, which is ignited by hot wire. the temperature change of the calorimeter and a known mass of water is measured

First Law of Thermodynamics

the total energy of the universe is constant

Entropy (S)

the disorder of a system

Second Law of Thermodynamics

all processes that occur spontaneously move in the direction of an increase in entropy of the universe

what is the entropy of the universe for a reversible process

0

what is the entropy of the universe for a spontaneous process

greater than 0

what are 4 rules that can be used to determine the change in entropy

entropy increases with an increse in molecules, temperature, when gas is formed from a liquid or solid, and when liquid is formed from a solid

enthalpy change (delta H)

the heat gained or lost by a system under constant-pressure conditions

when delta H is greater than 0 the reaction is

endothermic

when delta H is less than 0 the reaction is

exothermic

thermochemical equations are restricted to

moles

negative delta H values are usually associated with

spontaneous reactions

enthalpy change is dependent on the state of

matter

Hess’s law

if a reaction occurs in a series of steps, then the enthalpy change for the overall reaction is the sum of the enthalpy changes of the individual steps

state function

a function that only depends on the initial and final states and not the pathway

enthalpy change is a

state function

standard enthalpy of formation

change in enthalpy when 1 mol of the substance if formed from its elements when all substances are in their standard states

standard state of a gas

1 atm

stadard state of an aqueous solution

1 M

standard state of a pure substance

1 atm and 25 degrees C

standard molar entropies (S°)

entropies associated with 1 mol of a substance in its standard states

the standard enthalpy of formation of an element in its standard state is

0

Gibbs free energy (G)

thermodynamic function that combines enthalpy, entropy, and temperature

if delta G is greater than 0,

the reaction is not spontaneous

if delta G is less than 0,

the reaction is spontaneous

if delta G is equal to 0,

the reaction is at equilibrium

equation for delta G under nonstandard conditions

delta G° + 2.303 *RT* log *Q*

measurements needed in a thermodynamics experiment

mass, possible volume, initial and final temperature

energy

the capacity to do work or to produce heat

work

force acting over a distance

work equation

W=-P change in V

potential energy

due to position or composition (stored energy)

kinetic energy

energy due to motion of the object

state function

value that depends on the state of the substance, not how that state was reached

heat and temperature exchanges accompany which four processes?

heating and cooling a substance, phase change, dissolving solutes, chemical reactions

describe solute and solvent interactions in exothermic reactions

solute and solvent particles are more strongly attracted to each other than they are to themselves 

are bonds or attractive forces being formed or broken in exothermic reactions

formed

how does the temperature of the surrroundings change in exothermic reactions

increase

how does the temperature of the surrroundings change in endothermic reactions

decrease

are bonds or attractive forces being formed or broken in endothermic reactions

broken

describe solute and solvent interactions in endothermic reactions

solute and solvent particles are more strongly attracted to themselves than they are to each other

are decomposition reactions usually endo or exothermic?

endothermic

are synthesis reactions usually endo or exothermic?

endothermic

how can dissolving an ionic compound be both a physical and chemical change?

evaporation is a physical process, but bonds are boken which is a chemical process

intensive properties

properties independent of the amount of the substance

are specific and molar heat capacity intensive or extensive properties?

intensive

write an equation relating heat loss to heat gain

heat lost = -heat gained

how does the value of the heat of fusion for melting versus freezing?

heat of fusion is postive when melting and negative when freezing

describe the mathematical process when calculating the energy required to melt a substance

1. slope: q=mc delta T
2. straight line: q=(moles)(heat of fusion)
3. add up the values

equation for enthalpy

H=E+PV

bond enthalpy

energy stored in a chemical bond

standard heats of formation

the amount of heat needed to form 1 mole of a compound from its elements in their standard states

Hess’s law

if you add chemical equations to get an overall equation, then you can also add the heat changes to get the overall heat change

Internal Energy (E)

Internal Energy (E)