Thermodynamics and Thermochemistry formulas

Enthalpy ∆H

∆H = H products - H reactants

∆H > 0

endothermic (heat transferred from surroundings into system)

∆H < 0

exothermic (heat transferred from system to surroundings)

ΔE formula

∆E = q + w

ΔE = change in internal energy

q = heat

w = work

w formula

w = -P∆V

w = work

P = pressure (always positive)

ΔV = change in volume (Vfinal – Vinitial)

ΔV < 0

work done onto system

positive work

compression

ΔV > 0

work done by the system

negative work

expansion

+q

endothermic

-q

exothermic

+w

compression

-w

expansion

calculating heat absorbed or released

q = mCΔT

q = heat absorbed or released by the

substance (J)

m = mass of the substance (g)

C = specific heat capacity of the substance

(J•g-1•°C-1)

ΔT = change in temperature of the

substance (°C)

qsystem + qsurrounding =

0

qsystem =

-qsurrounding

calculating heat for phase changes

q = m∆Hfus/vap

q = heat absorbed or released by the

substance (J)

m = mass of the substance (kg)

∆Hfus = heat of fusion (J•kg-1)

∆Hvap = heat of vaporization (J•kg-1)

qrxn =

qrxn = heat of reaction (kJ)

-qcal

qcal = heat of calorimeter (kJ)

calorimeter formula

qcal = C∆T

qcal = heat of calorimeter (kJ)

C = heat capacity of calorimeter (kJ•°C-1)

∆T = change in temperature (°C)

heat released =

heat of combustion x mass

standard conditions

298 K, 1 atm, 1.0 M concentration

Bonds Broken =

Endothermic (∆H > 0)

Bonds Formed

Exothermic (∆H < 0)

∆H°rxn formula

∆H°rxn = Σ∆H°bonds broken – Σ∆H°bonds formed

∆H°bonds broken = change in bond enthalpies of

the reactants

∆H°bonds formed = change in bond enthalpies of

the products

formula to calculate for the enthalpy of

formation is as follows:

∆H°rxn = Σ(n•∆H°f products) – Σ(m•∆H°f reactants)

n = moles of products

m = moles of reactants

∆H°f products = enthalpy of formation of products

∆H°f reactants = enthalpy of formation of

reactants

Calculating entropy change

∆Srxn = Σ(n•Sproducts) – Σ(m•Sreactants)

n = moles of products

m = moles of reactants

Sproducts = entropy of the products

Sreactants = entropy of the reactants

∆Srxn > 0

reaction is entropically favorable;

products are more disordered than the

reactants.

∆Srxn < 0

reaction is entropically

unfavorable; products are more ordered than

the reactants.

Gibbs free energy

∆G = ∆H – T∆S | ∆G° = ∆H° – T∆S°

∆G = change in Gibbs free energy (kJ•mol-1)

∆H = change in enthalpy (kJ•mol-1)

T = temperature (K)

∆S = change in entropy (kJ•K-1•mol-1)

° - standard conditions

(298 K, 1 atm, 1.0 M concentration)

∆G < 0

exergonic

spontaneous

∆G > 0

endergonic

non spontaneous