Thermochemistry Study of energy changes as matter undergoes physical, chemical or nuclear transformations Warner – SCH 4U

Introduction Many activities involve energy physical changes melting, boiling,dissolving, etc. chemical reactions energy required or used during a reaction nuclear reactions nucleus of an atom split (fission) or joined (fusion)

What is Energy? Energy Kinetic energy (EK) Potential energy (EP) Energy due to motion Energy due to position (stored energy)

Systems & Surroundings In thermodynamics, the world is divided into a system and its surroundings A system is the part of the world we want to study (e.g. a reaction mixture in a flask) The surroundings consist of everything else outside the system SYSTEM CLOSED OPEN ISOLATED

OPEN SYSTEM: can exchange both matter and energy with the surroundings (e.g. open reaction flask, rocket engine, you) CLOSED SYSTEM: can exchange only energy with the surroundings (matter remains fixed) e.g. a sealed reaction flask, terrarium ISOLATED SYSTEM: can exchange neither energy nor matter with its surroundings (e.g. a thermos flask)

THERMAL ENERGY Total Potential and Kinetic Energy a sample of matter has.

Total Energy = Kinetic Energy + Potential Energy E = EK + EP Kinetic energy & potential energy are interchangeable Ball thrown upwards slows & loses kinetic energy but gains potential energy The reverse happens as it falls back to the ground

Heating Curve

Heating Curve Continued .

Temperature Measure of the average kinetic energy. When K.E increase, motion of particles increases and temperature increase. Kelvin  Celcius - 273 Celcius  Kelvin + 273 Thermometer used to measure temperature

Heat Energy Energy transformed from one substance to another due to temperature difference between them. Thermal Energy in Transit No instrument used to measure heat – must be calculated

UNITS OF ENERGY S.I. unit of energy is the joule (J) Heat and work ( energy in transit) also measured in joules 1 kJ (kilojoule) = 103 J Calorie (cal): 1 cal is the energy needed to raise the temperature of 1g of water by 1oC 1 cal = 4.184 J

Law of Conservation of Energy Heat lost by one substance equals heat gained by the other. Energy is not created or destroyed.

How to calculate HEAT!! m c t Factor Symbol Mass Specific Heat Capacity c Temperature t

Specific Heat Capacity Amount of heat required to raise the temperature of 1 gram of a substance 1oC. Units: J/goC or J/KgoC Molar Heat Capacity c x molar mass

Calculating Heat Heat (q) is measured in joules (J) q = m c ΔT q = heat m = mass (g) ΔT = change in temp (°C) c = specific heat capacity (J/g °C)

Heat lost/gained when substances are added together. - q (lost) = + q (gained) - (mcΔt) = + mcΔt