Thermochemistry

Thermochemistry All changes in matter, both physical and chemical, involve changes in energy Thermochemistry is the study of energy changes is physical and chemical processes

Energy All forms of energy can be classified as either: Kinetic Energy - energy of motion Potential Energy - stored energy SI unit = joule (J) = kg·m2/s2 1 J is approximately the amount of energy required to lift an apple 1 m (very small!) so often expressed as kJ (1000 J) 1 calorie = 4.184 J

System & Surroundings System: substances in which a change (physical or chemical) occurs e.g. reactants and products Surroundings: Everything else in the universe! Usually only consider anything nearby that is capable of exchanging energy or matter

Endothermic & Exothermic Endothermic Processes: Heat is absorbed by the system from the surroundings Feels cold Exothermic Processes: Heat is released from the system into the surroundings Feels hot

Energy, Temperature & Heat Thermal Energy: The sum of all kinetic energies of all the particles in a system. Cannot be measured. Temperature: A measure of the average kinetic energy of all the particles in a system. Can be measured. Heat: Kinetic energy transferred between substances. I.e. an object cannot possess heat.

Heat Capacity Heat Capacity: Amount of heat required to raise the temperature of a substance of any mass by 1˚C. C = J/˚C Specific Heat Capacity: Amount of heat required to raise the temperature 1 g of a substance by 1˚C. c = J/g•˚C You are provided with a glass of milk and a swimming pool of milk. Which will have the higher heat capacity? Which will have the higher specific heat capacity? Molar Heat Capacity: Amount of heat required to raise the temperature 1 mole of a substance by 1˚C. c = J/mol•˚C

Factors that Affect Heat Mass - the greater the number of particles, the more heat required Type of Substance - each substance has a different specific heat capacity Temperature Change - the greater the temperature change the more heat required Q = mc∆T

Calculating Heat When a 1.25 kg sample of water was heated in a kettle, its temperature increased from 16.4˚C to 98.9˚C. How much heat did the water absorb? Q = mc∆T Q = ? m = 1.25 kg c = 4.18 J/g•˚C ∆T = T2 - T1 = 98.9˚C - 16.4 ˚C = 82.5˚C

Practice p. 300 #1-5 p. 302 #8-13 p. 305 #1-6 Specific Heat Capacity Worksheet