1. THERMOCHEMISTRY The study of heat released or required by chemical reactions Fuel is burnt to produce energy - combustion (e.g. when fossil fuels are burnt) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) + energy

2. What is Energy? Energy Kinetic energy (E K ) Potential energy (E P ) Energy due to motion Energy due to position (stored energy)

3. Total Energy = Kinetic Energy + Potential Energy E = E K + E P 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

4. Law of Conservation of Energy Law of Conservation of Energy: the total energy of the universe is constant and can neither be created nor destroyed; it can only be transformed. internal energy The internal energy, U, of a sample is the sum of all the kinetic and potential energies of all the atoms and molecules in a sample i.e. it is the total energy of all the atoms and molecules in a sample

5. HEAT and WORK HEAT is the energy that transfers from one object to another when the two things are at different temperatures and in some kind of contact e.g. kettle heats on a gas flame cup of tea cools down (loses energy as heat) Thermal motion (random molecular motion) is increased by heat energy i.e. heat stimulates thermal motion

6. 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) = 10 3 J Calorie (cal): 1 cal is the energy needed to raise the temperature of 1g of water by 1 o C 1 cal = 4.184 J

7. EXOTHERMIC & ENDOTHERMIC REACTIONS Exothermic process: a change (e.g. a chemical reaction) that releases heat. Exothermic process:  H < 0 Burning fossil fuels is an exothermic reaction

8. Endothermic process: a change (e.g. a chemical reaction) that requires or absorbs heat. Endothermic process:  H > 0 Photosynthesis is an endothermic reaction (requires energy input from sun) Forming Na + and Cl - ions from NaCl is an endothermic process

9. Measuring Heat reaction Exothermic reaction: heat given off & temperature of water rises Endothermic reaction: heat taken in & temperature of water drops

10. How do we relate change in temp. to the energy transferred? Heat capacity (J/ o C) = heat supplied (J) temperature ( o C) Heat Capacity = heat required to raise temp. of an object by 1 o C more heat is required to raise the temp. of a large sample of a substance by 1 o C than is needed for a smaller sample

11. Specific heat capacity is the quantity of energy required to change the temperature of a 1g sample of something by 1 o C Specific Heat Capacity (Cs) Heat capacity Mass = J / o C / gJ / o C g =

12. Vaporization Energy has to be supplied to a liquid to enable it to overcome forces that hold molecules together endothermic process (  H positive) Melting Energy is supplied to a solid to enable it to vibrate more vigorously until molecules can move past each other and flow as a liquid endothermic process (  H positive) Freezing Liquid releases energy and allows molecules to settle into a lower energy state and form a solid exothermic process (  H negative) (we remove heat from water when making ice in freezer)

13. Chemical Reactions All chemical reactions either release or absorb heat Exothermic reactions: Reactants products + energy as heat (  H -ve) Endothermic reactions: Reactants + energy as heat products (  H +ve) e.g. burning fossil fuels e.g. photosynthesis