thermodynamics things to know

ΔH equation

ΔH= ∑ΔH_prod - ∑ΔH_react

ΔG equation

ΔG= ΔH-TΔS

ΔS equation

ΔS= ΔH/T

ΔS units

JxK

ΔH units

KJ/mol

when calculating ΔG, what must ΔS be changed to

must be converted from J/K to KJ/K

how do you convert ΔS from J/K to KJ/K

multiply by 1000

the opposite- how do you convert J/K to KJ/K

divide by 1000

when ΔG is negative the reaction is..

always spontaneous (thermodynamically favorable)

when a beaker is colder than before the reaction is..

endothermic

when a beaker is warmer than before the reaction is..

exothermic

what is an endothermic reaction

energy/heat absorbed into the system

what is an exothermic reaction

energy/heat released into the surroundings

what is the system

the chemical reaction

when potential energy decreases..

energy is given off in the form of heat (exothermic)

when energy is released it causes the temp of the surroundings to..

increase

when energy is absorbed it causes the temp of the surroundings to..

decrease

what are the 3 different ways to calculate ΔH

1. using bond enthalpies (ΔH= ∑bonds broken- ∑bonds formed)

2. using heats of formation (ΔH_rxn=∑ΔH_prod - ∑ΔH_react)

3. Hess’s law (can be figured out ONLY if there’s steps)

energy is always..

positive!!!

energy absorbed or released is..

proportional to moles

entropy is…

disorder

+ΔS

disorder increased

-ΔS

disorder decreased

ΔS_rxn equation

ΔS_rxn=∑ΔS_prod - ∑ΔS_react

temperature must be converted to _______ while calculating ΔG

kelvin

-ΔG means

the reaction is always spontaneous

+ΔG means

the reaction is never spontaneous

-ΔH, +ΔS, -ΔG

always spontaneous

-ΔH, -ΔS, -ΔG

favorable @ low temps

exothermic

spontaneous

+ΔH, +ΔS, -ΔG

favorable @ high temps

endothermic

spontaneous

+ΔH, -ΔS, +ΔG

never occurs

when a reaction is exothermic

ΔH drives it

when a reaction is endothermic

ΔS drives it

what does BARF mean

break absorbs, forms release

-ΔH has ______ reactants but _______ products

weaker, stronger

+ΔH has ______ reactants but _______ products

stronger, weaker

activation energy?

energy required to start a reaction

if ΔG is negative but no reaction occurs the activation energy is..

large

low specific heat means

it changes temp easily and does not store heat

high specific heat means

it changes temp slower and stores heat well

when solving for ΔS, temp must be converted to

kelvin

when solving for ΔS, KJ must be converted to

J

aqueous solutions..

ΔS>0

if a reactant dissolves, ΔG is..

negative

endothermic..

ΔH>0

spontaneous reactions are..

thermodynamically favorable with a release of free energy

formation..

solute and solvent become more stable and go into lower energy levels which makes it an exothermic reaction