thermo master

First Law of Thermodynamics

Energy is conserved: \Delta U = q + w

q in thermodynamics

Heat transferred into or out of a system.

w in thermodynamics

Work done on or by the system.

\Delta U

Change in internal energy of the system.

Formula for work by expansion/compression

w = -P \Delta V

Equation for heat transfer without a phase change

q = mc\Delta T

Enthalpy (H)

Heat content at constant pressure: H = U + PV

Calculation of \Delta H

\Delta H = \sum \Delta Hf^\circ(\text{products}) - \sum \Delta Hf^\circ(\text{reactants})

Entropy (S)

Measure of disorder; units = J/K or J/mol·K

How to calculate \Delta S

\Delta S = \sum S^\circ(\text{products}) - \sum S^\circ(\text{reactants})

Gibbs Free Energy formula

\Delta G = \Delta H - T\Delta S

Meaning of \Delta G < 0

The reaction is spontaneous.

Meaning of \Delta G = 0

The system is at equilibrium.

Relationship between \Delta G^\circ and K

\Delta G^\circ = -RT \ln K

Temperature unit in thermodynamics

Kelvin (K)

Formula for heat during a phase change

q = n \Delta H_{phase}

Difference between q at constant pressure vs. constant volume

qp = \Delta H; qv = \Delta U

Pressure-volume work to joules

1 \text{L·atm} = 101.3 \text{J}

Ideal gas law equation

PV = nRT

Equation relating Kp and Kc

Kp = Kc(RT)^{\Delta n}

R in J/mol·K

R = 8.314 \text{J/mol·K}

R in L·atm/mol·K

R = 0.0821 \text{L·atm/mol·K}

Meaning of positive \Delta S

More disorder or randomness in the system.

Hess’s Law

The total enthalpy change is the sum of individual steps.

Phase change occurrence

When temperature remains constant while heat is added or removed.

Standard \Delta H{vap} and \Delta H{fus} of water

\Delta H{vap} = 40.7 \text{kJ/mol}, \Delta H{fus} = 6.01 \text{kJ/mol}

Determine spontaneity from \Delta H and \Delta S

Use the spontaneity table with \Delta G = \Delta H - T\Delta S

Unit of heat capacity

J/g·K or J/mol·K

Sign of q if the system releases heat

q < 0

Sign of w when the system expands against a piston

w < 0