1. EQUILIBRIUM REACTION RATES + ENERGY

2. Chemical energy of a substance = potential + kinetic energy. Kinetic energy = doing energy (mechanical) Potential energy = stored energy

3. What these energies result from Attractions between electrons and protons Repulsion between nuclei Repulsion between electrons Movement of electrons Vibration and rotation of nuclei

4. Enthalpy Is the Chemical energy of a substance is sometimes also called its HEAT CONTENT given the sign H

5. Exothermic When H (products) < H (reactants) Energy is released into environment Feels Hot Eg burning of petrol energy reactants products Energy released ΔH negative

6. Endothermic When H (products) > H (reactants) Energy is absorbed from environment around the reactants Feels cooler energy reactants products Energy absorbed ΔH positive

7. ΔH – Delta H ΔH = energy (products) – energy (reactants) The energy released or absorbed in a chemical reaction is called the HEAT OF REACTION This heat of reaction is the difference in the enthalpy’s of the products and reactants (hence ΔH)

8. Examples Exothermic reactions –Burning of fuels including food Endothermic reactions –Photosynthesis (absorbs energy from sunlight to convert H 2 O and CO 2 into glucose and O 2

9. Thermochemical equations Show the energy released or absorbed durin a chemical reaction Energy is measured in Joules (J) or kilo joules (kJ) The heat of reaction (ΔH ) has the units j mol –1 of kJ mol –1 The energy is therefore related to the number of moles as given by the equation

10. Exercises CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) ΔH = –890 kJ mol –1 2CH 4(g) + 4O 2(g)  2CO 2(g) + 4H 2 O (g) ΔH = 2(–890 kJ) = –1780 mol –1 CO 2(g) + 2H 2 0 (g)  CH 4(g) + 2O 2(g) ΔH = 890 kJ mol –1 (reverse reaction – reverse sign)

11. Chemical bonds during a chemical reaction Bonds in the reactants must first be broken –This requires energy to be absorbed New bonds are created in the products –This requires energy to be released

12. Activation energy The energy required to break bonds in the reactants so that the reaction can proceed.

13. Energy profile Exothermic energy reactants products ΔH Activation energy Energy released as bonds break Energy released as bonds form

14. Energy profile Endothermic reactants products ΔH Activation energy

15. Factors affecting rate of a reaction Increasing the surface area of solids Increasing concentration of reactants or pressure of gases Increasing temperature Adding a catalyst

16. Factors affecting rate of a reaction Increasing the surface area of solids –Breaking reactant into smaller pices increases the surface area –More particles are present on the surface –The greater number of particles exposed allows for greater number of collisions with other reactant particles

17. Factors affecting rate of a reaction Increasing concentration of reactants or pressure of gases –A greater number of particles moving in a given volume of solution will mean a greater chance of collision between particles

18. Factors affecting rate of a reaction Increasing temperature –As temperature increases the average speed and kinetic energy of particles increases –This results in a greater chance of collisions occurring

19. A Catalyst A substance that will increase the rate of a chemical reaction without being consumed in that reaction - 2 Types Homogenous –Same state as the reactants eg Atmospheric reactions Heterogeneous –Different state to the reactants –Easier to separate out at the conclusion of reaction

20. How catalysts work Haber process –N 2(g) + 3H 2(g) 2NH 3 (g) ΔH = –91 kJ mol –1 –Catalysed with powdered Iron –N 2 and H 2 absorb onto surface of Fe –As they absorb, bonds within them break –N and H molecules now readily form NH 3 molecules and move away from Fe

21. Energy profile diagram change when a catalyst is used N 2(g) + H 2(g) energy ammonia Without catalyst With catalyst Energy needed to break bonds is LESS ΔH