AP Chem Unit 6

Skinner 2026-27

enthalpy is _ for exo/endo

negative for exothermic, positive for endothermic

system

the part of the world you are studying, can be beaker/salt/water/etc

surroundings

everything around the system, can be air/table/hands, etc

universe

system + surroundings together

heat (q)

amount of thermal energy transferred

work

energy needed to move something against a force, typically expanding gases or a piston

work equation

work= -PΔV

endothermic

• heat absorbed by system from surroundings

• phase changes: melting/boiling/vaporizing/sublimating

• changes that involve breaking/separation

exothermic

• heat is released from system to surroundings

• phase changes: freezing/condensation/deposition

• changes that involve combining

dissolving can/can’t be endothermic OR exothermic

can

solvent/solute must expand by overcoming IMFs- this is a __ process

endothermic

solute and solvent must recombine- this is a __ process

exothermic

when we measure temperature change of solution, we measure change of ___

surroundings

enthalpy of reaction (ΔH)

difference in energy of products and energy of reactants

activation energy

• used to break bonds + IMFs

• energy released comes from forming bonds

• can be endo or exo

catalyst

• added to increase rxn rate

• not consumed

• ΔH is NOT CHANGED

when hotter particles are in contact withe one another and collide, energy is __, resulting in hotter particles__energy and colder substance _ in temp

transferred, losing, increasing

thermal equilibrium

2 substances reach the same temp, have SAME average KE

units for q

J or calories

3 factors contribute to the amount of heat transferred

mass, specific heat capacity, and ΔT

specific heat capacity

amount of energy needed to raise temperature of one gram of a substance by one degree Celsius

units for c

J/g degrees C

water specific heat capacity

4.18 J/(g·°C)

calorimeter

measures heat transferred during a rxn, stops the transfer of heat between inside and surroundings

1st law of thermodynamics

energy cannot be created/destroyed, must be conserved. so, heat lost = heat gained.

q(metal) = -q(water) represents what law

1st law of thermo

3 main processes of energy changes

• heating/cooling

• phase transitions

• chemical rxns

during phase change there is/is not a temp change

is not- energy used to change particle positions

2 main effects of heat energy supplied

• to increase KE, which increases average speed and temp

• to overcome IMFs, which does not effect speed and temp (often called latent heat)

constant pressure calorimeter

outer cup insulates, 2 solutions mixed, heat produced/absorbed by rxn determined

constant-volume bomb calorimeter

• filled with oxygen gas and put in a bucket

• electrically ignited, head measured with water ∆T

• used to determine calories

1 calorie = __kJ

4.18 kJ or 4180 J

at constant pressure, ∆H = __

Q

breaking bonds requires/releases energy

requires

forming bonds requires/releases energy

releases

to find potential energy change…

add bond breaking and forming energies and compare. if breaking > making = exo and vice versa

bond energy

enthalpy change required to break or form given bond in 1 mole of gas

Basket Ball is My Best Friend

Bonds Broken Minus Bonds Formed

standard enthalpy

∆H°, tells standard state (1 mol, 1 ATM, 298K)

rxn or f indicate __ of enthalpy

type

∆H°f

energy change when forming 1 mole

∆H°rxn

energy change for a reaction

enthalpy of reaction =

sum of formation energies of products- sum of formation energies for rxn

Hess’s law property 1

heat = products- and reactants

hess’s law property 2

if the reaction is reversed, the sign of q is reversed but amount stays the same

hess’s law property 3

going from one set of reactants to a set of products, change is always the same regardless of the route taken

route 3 describes ___

state functions