A student investigates the reaction between excess calcium carbonate granules (CaCO3\text{CaCO}_3CaCO3) and 50.0 cm3 of 0.500 mol dm-3 hydrochloric acid (HCl\text{HCl}HCl) at 298 K:
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g) \text{CaCO}_3(\text{s}) + 2\text{HCl}(\text{aq}) \rightarrow \text{CaCl}_2(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g}) CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)The volume of carbon dioxide gas produced is recorded over time and plotted as Curve I in the graph below.
The experiment is repeated under identical conditions, but a small quantity of a suitable catalyst is added. The results are plotted as Curve II.
Which of the following statements correctly explains the differences between Curve I and Curve II?
The catalyst increases the mean kinetic energy of the reactant molecules, resulting in Curve II's steeper initial gradient, but does not alter the final volume of gas VmaxV_{\text{max}}Vmax.
The catalyst increases the value of the activation energy for the reaction, meaning Curve II reaches the maximum volume VmaxV_{\text{max}}Vmax in a shorter time.
The catalyst provides an alternative pathway with a lower activation energy, increasing the rate and resulting in Curve II's steeper initial gradient, whilst the total volume of CO2\text{CO}_2CO2 remains VmaxV_{\text{max}}Vmax.
The catalyst is consumed during the initial stages of the reaction to produce more intermediate gas, causing Curve II to plateau at a volume greater than VmaxV_{\text{max}}Vmax.
Practise Edexcel GCSE Chemistry Rates of reaction with exam-style questions for Foundation and Higher tier. 166 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
