SASS Chem Speed of Rxn AfL Ans

Page 1 ST ANDREW’S SECONDARY SCHOOL NAME TEACHING GROUP CHEMISTRY (G3) 17.1 Measuring Speed of Reaction SPEED OF REACTION Assessment for Learning 1 [A] • Marble chips is also known as limestone, calcium carbonate (CaCO3). 2 [A] • Experiment investigates the rate of reaction by measuring the mass loss from the reaction. • Mass loss = CO2 produced. • Cotton wool prevents the acid used from leaving the conical flask, at the same time allowing CO2 gas to leave. 3 [B] • Mass loss corresponds to the decrease in mass measured by the balance. • Mass will not decrease to 0 g. 4 [D] • No effervescence observed as the reaction did not proceed. • H2SO4 forms a barrier from the ppt. produced around CaCO3, thereby preventing any H+ (aq) from reaction. CaCO3 (s) + H2SO4 (aq) ® CaSO4 (s) + CO2 (g) + H2O (l) 5 [A] • Combustion releases thermal energy. • As the combustion proceeds, more thermal energy is produced. Remaining reactants will gain the thermal energy produced, thereby increasing the speed of reaction. 6 [A] • The use of gas syringe suggests a gas (H2) produced. 7 [C] • Mass increases as magnesium gains oxygen from air during oxidisation. 2 Mg + O2 ® 2 MgO 8 [B] • Gas produced is H2. M + 2 HCl ® MCl2 + H2 • H2 gas is insoluble in water. Apparatus 1 is not suitable: H2 gas is less dense than air (Mr of H2 = 2; Mr of air ≈ 28). SOLUTIONS

Page 1 ST ANDREW’S SECONDARY SCHOOL NAME TEACHING GROUP CHEMISTRY (G3) 17.2 Factors Affecting Speed of Reaction SPEED OF REACTION Assessment for Learning 1 [D] • Increasing both the concentration and temperature of acid will increase the rate of reaction. 2 [B] • Decreasing the temperature = Reacting particles loses thermal energy. Option A: Decreasing particle size = ↑ Surface area to volume ratio. Option C: Decreasing the volume of the conical flask = ↑ Concentration of the acid. Concentration ↑ = No. of molesVolume ↓ Option D: Using 1.5 mol/dm3 nitric acid = ↑ Concentration of the acid. 3 [D] • Using Mg ribbon = ↓ surface area to volume ratio. 1: Heating Mg = ↑ Thermal energy to the reacting particles. 2: Using a higher proportion of O2 in air = ↑ Amount of reacting O2. 4 [D] • Increasing temperature of reaction = ↑ Rate of reaction. Option B is wrong: Rate of reaction continues to increase with increasing temperature. Rate does not stay constant after reaching a certain temperature. 5 [A] • Increasing the concentration of the reactants = ↑ No. of reacting particles. • Increasing the temperature = ↑ Thermal energy. • Increasing the volume of H2SO4 = ↑ No. of reacting particles. (No. of moles = Concentration × Volume) 2: Increasing the size of the pieces of MgCO3 = ↓ Surface area to volume ratio = ↓ Speed of reaction. 6 [D] • ↑ Pressure of the reaction = ↓ Space between the reacting gaseous particles. Option A: No change in speed of reaction. Option B: ↓ No. of reacting particles. Option C: ↓ Temperature of the reaction. 7 [A] • Rate of reaction for Y is higher than that for X. Both X and Y produce the same volume of H2 gas. • The use of catalyst will not change the amount of products formed. Option B: A lower higher temperature is used in Y. Option C: Larger Smaller pieces of zinc are used in Y. Option D: Less More concentrated acid is used in Y. SOLUTIONS ↑ Speed of Rxn ↑ Speed of Rxn

Page 2 8 [D] • The catalyst, MnO2, does not decrease the activation energy of the reaction; however, it provides an alternative pathway with a lower activation energy for the reactants to react. 9 [B] • Catalysts are usually transition metals or the compounds of transition metals. 10 [C] 11 [B] 12 [B] • The catalyst does not decrease the activation energy of the reaction; however, it provides an alternative pathway with a lower activation energy for the reactants to react. Activation energy, EA = the energy barrier that the particles have to overcome in order to react.