RI Y3 Chem 2022 FE Revision Energetics Kinetics Equilibrium ANS.pdf

1 Raffles Institution Raffles Programme Year Four Chemistry Name: ____________________________ ( ) Class: ______ Date: _______ 2022 FE Revision – Chemical Energetics, Reaction Kinetics, Equilibrium ANSWERS Chemical Energetics Exothermic Process Endothermic Process 1 heat is released heat is absorbed 2 enthalpy change (ΔH) value is negative enthalpy change (ΔH) value is positive 3 the container/surroundings feels hot the container/surroundings feels cold 4 bond making bond breaking 5 energy content of products < energy content of reactants energy content of products > energy content of reactants 6 e.g. combustion, neutralization, respiration, freezing e.g. photosynthesis, thermal decomposition, melting Practice Question 1 (a) C6H12O6 + 6O2(g)  6CO2(g) + 6H2O(l) (b) (i) During respiration, energy is absorbed to break the bonds in C 6H12O6 and the O=O bonds of oxygen. Energy is released when the C=O bonds of carbon dioxide and the O-H bonds of water are formed. The reaction is exothermic because the amount of heat released is greater than the amount of heat absorbed. (ii) C6H12O6 + 6O2 6H2O + 6CO2 Ea ∆H progress of reaction energy

2 (iii) ∆H = energy absorbed – energy released for bond breaking by bond making = [+9546 + 6(496)] – [6(2x740) + 6(2x460)] = −1878 kJ Reaction Kinetics 1 Every reaction has an activation energy (E a), which is the minimum energy that colliding particles must possess in order to result in a reaction. The smaller the Ea the faster the reaction. 2 Factors that increase the speed of a reaction: factors collision theory explanation increase temperature this increases the number of reactant particles having the Ea, causing particles to collide harder and more frequently increase pressure (only for gases) this causes particles to be closer thus more frequent effective collisions between them increase concentration this causes more particles per unit volume thus more frequent effective collisions between reactant particles increase surface area (by decreasing particle size) this causes more frequent effective collisions between reactant particles presence of a catalyst • this provides an alternative pathway with a lower Ea, resulting in more reactant particles having the Ea thus more frequent effective collisions between them 4 Increasing the temperature, pressure, surface area or catalyst would increase the slope (gradient) of the graph but the amount of product would finally still be the same as that of the control experiment. However, increasing concentration MAY result in inc reased speed as well as increased amount of products, since the initial amount of reactant is also increased when its concentration is increased. Practice Questions 1 (a) CuCO3 (s) + 2HCl (aq)  CuCl2 (aq) + H2O (l) + CO2 (g) (b) (b)

3 (c) D