# All the symbols!

• q - heat needed

• ΔT - Temperature change

• ΔH - Enthalpy change

• ΔH° - in standard conditions

• ΔS - Entropy change

• R - Gas constant (8.314 J/Kmol)

• K - Dissociation rate

• ΔG - Gibbs free energy / available energy

• ΔG° - in standard conditions

## q (Heat)

• q = mcΔT

• q - heat needed (J)

• m - mass of object releasing or absorbing - usually water (4.184 J / gC)

• ΔT - temperature change (C)

## Molar Heat

• ΔH = q / moles

• q - heat (J)

• ΔH - Enthalpy change (J/mol)

• Products - reactants

• Coefficient(enthalpy of formation) - coefficient(enthalpy of formation)

• You are given the equation and enthalpy of formation for each.

• Meaning of ΔH

ΔH > 0 (endothermic / temp of reaction decreases)

ΔH < 0 (exothermic / temp of reaction increases)

ΔS > 0 (increase in entropy)

ΔG < 0 at high temperaturesΔG > 0 at low temperaturesSpontaneous at high temperatures.

ΔG < 0Spontaneous

ΔS < 0 (decrease in entropy)

ΔG > 0Nonspontaneous

ΔG < 0 at low temperaturesΔG > 0 at high temperaturesSpontaneous at low temperatures.

## ΔG (Gibbs Free Energy)

• ΔG = ΔH - TΔS

• ΔG - change in free energy (kJ)

• ΔH - change in enthalpy (kJ)

• T - absolute temperature (K)

• ΔS - change in entropy (kJ/K)

• Units can change. Make sure ΔH has same units as ΔS. ΔH is given in kJ/mole + ΔS in J/mole

• ΔG° = -RTln(K)

• ΔG° applies to standard-state conditions while ΔG is gibbs free energy given certain condition

• K - [C][D]/[A][B]

• T - temperature (K)

• R - constant (8.314 J / mole K)

• Meaning of ΔG

• Gibb’s free energy.

• ΔG < 0 is thermodynamically favored and exothermic.

• ΔG > 0 is not thermodynamically favored and endothermic.

## Hess’s Law

Hard to explain. Please click the title in order to watch a short video on Hess’s Law Problems.

## ΔS - Change in Entropy

• Increases as you go from solid to aqueous to liquid to gas

• ΔS = Np(sum of products) - Nr(sum of reactants)

• Np = coefficient of products

• Nr = coefficient of reactants

## Coupled Reactions

• Two reactions that share a common intermediate (a product of one reaction is the reactant of another).

• Usually combined with Hess’s law to determine free energy change, ΔG, for the coupled reaction.

## Heat of reaction / heat of solution

• The heat of solution is the amount of heat absorbed or released when a solute dissolves in a solvent, while the heat of reaction is the amount of heat absorbed or released during a chemical reaction. The heat of solution is specific to the dissolution process, while the heat of reaction is specific to the chemical reaction taking place.

• Heat of solution

• HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

## Enthalpy diagram with catalyst

• ΔH is the change between starting and ending energy.

• Energy of activation is the change in starting energy to the peak.

• Starting energy is where the graph starts.

• Endothermic reactions have a higher ending energy than starting energy. Exothermic reactions have a lower ending energy than starting energy.

## Maxwell Boltzmann

• Higher temperatures move the graph peak right and down.

## Lattice Enthalpy

• Bigger charge triumphs size. Smaller size wins if have same charge.

## Drivers

Temperature Change

ΔH

ΔS

Driver

-

-

Enthalpy (G→L→S)

+

+

Entropy (S→L→G)

-

+

Both

• A reaction is favored if enthalpy decreases.