Thermochemistry The study of the changes in heat energy that accompany chemical reactions and physical changes

Thermochemistry Heat a form of energy. can be transferred between samples heat flows from matter at a higher temperature to matter at a lower temperature Temperature a measure of the average kinetic energy of the particles in a sample.

Thermochemistry Units of Heat Joule (SI unit) calorie cal the amount of energy required to raise the temperature of one gram of water one degree Celsius. Calorie Cal a dietary calorie. kilocalorie, kcal (1,000 calories)

Thermochemistry Enthalpy the heat content of a system represented by H only changes in enthalpy can be measured ∴ ΔH is used

Thermochemistry Specific heat capacity, c p the amount of energy required to raise the temperature of one gram of a substance one degree Celsius used in equation q = m x c p x ΔT

Thermochemistry q = m x c p x ΔT note that in the Metric System, Joules are the unit of measure for heat. Energy, or heat (J) mass (g) Δ temp (°C) specific heat (J/g°C)

Heat capacity, c p

q = m x c p x ΔT 1.A 45.0-gram sample of iron is heated from 25.0°C to 50.0°C. How much energy is required? (c p iron = J/g°C) q = ? m = 45.0 g c p = J/g°C ΔT = 50.0°C – 25.0°C = 25.0°C q = m c p ΔT q = 45.0g (0.449 J/g°C) (25.0°C) = q = 505 J

2. What is the specific heat capacity of an object if a 12.5-gram sample is heated from 12.0°C to 28.0°C using joules? q = J m = 12.5 g c p = ? ΔT = 28.0 – 12.0 = 16.0°C q = m c p ΔT