A student investigated the rate of reaction between calcium carbonate chips and excess dilute hydrochloric acid:
CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)\text{CaCO}_3\text{(s)} + 2\text{HCl(aq)} \rightarrow \text{CaCl}_2\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
The volume of carbon dioxide gas collected was measured over time. The student plotted a graph of the volume of carbon dioxide collected in cm3\text{cm}^3cm3 against time in seconds.
To determine the rate of reaction at t=45 st = 45\text{ s}t=45 s, a tangent was drawn to the curve at that point. The tangent line passes through the coordinates (15 s,24 cm3)(15\text{ s}, 24\text{ cm}^3)(15 s,24 cm3) and (75 s,63 cm3)(75\text{ s}, 63\text{ cm}^3)(75 s,63 cm3).
Calculate the rate of reaction at t=45 st = 45\text{ s}t=45 s. Give your answer to 2 significant figures and include the units.
Explain, in terms of collision theory, why the rate of reaction decreases and eventually becomes zero.