Chapter 16 Thermochemistry

Thermochemistry

Study of the transfers of energy as heat that accompany chemical reactions and physical changes

Calorimeter

Energy absorbed or released as heat in a chemical or physical change is measured in a calorimeter

Temperature

Measure of the average kinetic energy of the particles in a sample matter.

Joule

The SI unit of heat as well as all other forms of energy

Heat

Energy transferred between samples of matter because of a difference in their temperatures

Specific Heat

Amount of energy required to raise the temperature of one gram of a substance by one Celsius degree or one kelvin (because the sizes of the degree divisions on both scales are equal)

Specific Heat Formula

C_p = q/m x ΔT

Energy Lost or Gained Formula

q = c_p × m × ΔT

C_p

Specific Heat

q

Energy lost or gained

m

mass of the sample

ΔT

Change in temperature

Enthalpy Change

The amount of energy absorbed by a system as heat during a process at constant pressure. Tells you whether heat is released or absorbed (kJ)

ΔH < 0 —> Exothermic (Release Heat)
ΔH > 0 —> Endothermic (Absorb Heat)

Enthalpy of Reaction

Quantity of energy transferred as heat during a chemical reaction

Thermochemical Equation

Equation that includes the quantity of energy released or absorbed as heat during the reaction as written

ex. 2H₂ (g) + O₂ (g) —> 2H₂O (g) + 483.6 kJ

Molar Enthalpy of Formation

The enthalpy change that occurs when one mole of a compound is formed from its elements in their standard state at 25C and 1 atm

Enthalpy of Combustion

The enthalpy change that occurs during the complete combustion of one mole of a substance

Hess Law

If the reaction happens in steps, you can add up the ΔT values of those steps to get the total ΔT for the reaction

Entropy (S)

Qualitative way as a measure of the degree of randomness of the particles, such as molecules, in a system.

Solid - Low Entropy - Particles tightly packed and ordered

Liquid - Medium Entropy - Particles are more spread out and move

Gas - High Entropy - Particles are far apart and move freely

Free Energy (G, Gibbs free energy)

Combined enthalpy-entropy function to tell the amount of usable energy available after, and tell if the reaction is spontaneous.

ΔG < 0 = Spontaneous

ΔG > 0 = Nonspontaneous

ΔG = 0 —> Equilibrium

Free-Energy Change

ΔG, of a system is defined as the difference between the change in enthalpy, ΔH, and the product of the Kelvin temperature and the entropy change, which is defined as TΔS

Free Energy Change Formula

ΔG = ΔH - TΔS

G = Gibbs Energy (kJ)

H = Heat Energy (kJ)

T = Change in Temperature (kJ)

S = Entropy (kJ/K)