Comprehensive Notes on Calcium Carbonate and Hydrochloric Acid Reactions

The chemical reaction between calcium carbonate and hydrochloric acid is defined by the following balanced equation: $CaCO_3(s) + 2HCl(aq) \rightarrow CaCl_2(aq) + CO_2(g) + H_2O(l)$
The reactants involved are solid calcium carbonate chips ( $CaCO_3(s)$ ) and an aqueous solution of hydrochloric acid ( $HCl(aq)$ ).
The products generated include aqueous calcium chloride ( $CaCl_2(aq)$ ), carbon dioxide gas ( $CO_2(g)$ ), and liquid water ( $H_2O(l)$ ).
The progress of this reaction is monitored by measuring the volume of carbon dioxide gas produced. This gas is collected using an inverted measuring cylinder as it displaces the contents within the cylinder.

The volume of carbon dioxide ( $CO_2$ ) in the measuring cylinder increases over time as the reaction proceeds because products are continuously being formed by the interaction of the reactants.
The reaction is described as exothermic, leading to an increase in temperature. This thermal energy influences the kinetic energy of the particles.
Changes in state and rate are driven by the collisions per unit of time/volume, represented in the transcript as ‘the waves the collisions per unit extend’ to absorb the heat and reach the rate of product mission.

Initial Rate of Reaction: At the start of the reaction, the graph shows its steepest gradient. This indicates the highest rate of reaction because the concentration of hydrochloric acid ( $HCl$ ) and the available surface area of the calcium carbonate chips ( $CaCO_3$ ) are at their maximum. This leads to the highest frequency of successful collisions between reactant particles per unit of time.
Mid-Reaction Progress: As the reaction continues, the curve of the graph becomes less steep. This represents a slowing rate of reaction. The concentration of the reactive particles decreases as they are converted into products, which results in a lower frequency of effective collisions.
End of the Reaction: Finally, the graph levels off and becomes a horizontal line (plateaus). This indicates that the reaction has reached completion and the rate of reaction is now zero. This occurs because at least one of the reactants, either the calcium carbonate or the hydrochloric acid, has been completely consumed, and no further carbon dioxide gas can be produced.

An experiment compares two specific setups involving $5.00\,g$ of calcium carbonate ( $CaCO_3(s)$ ) and $100\,cm^3$ of hydrochloric acid ( $HCl(aq)$ ). Both setups utilize calcium carbonate in powder form instead of chips to maximize surface area.
Reaction One Parameters:
- Mass of $CaCO_3(s)$ : $5.00\,g$ (powder)
- Concentration of $HCl(aq)$ : $0.500\,mol\,dm^{-3}$
- Volume of $HCl(aq)$ : $100\,cm^3$
Reaction Two Parameters:
- Mass of $CaCO_3(s)$ : $5.00\,g$ (powder)
- Concentration of $HCl(aq)$ : $2.00\,mol\,dm^{-3}$
- Volume of $HCl(aq)$ : $100\,cm^3$

Rate Comparison: Reaction Two will have a significantly higher initial rate of reaction compared to Reaction One. This is because Reaction Two utilizes a higher concentration of hydrochloric acid ( $2.00\,mol\,dm^{-3}$ vs. $0.500\,mol\,dm^{-3}$ ). Increased concentration means there are more reactant particles ( $H^+$ and $Cl^-$ ions) per unit volume ( $dm^3$ ), increasing the probability and frequency of successful collisions with the calcium carbonate powder.
Total Volume of Gas Produced:
- In Reaction One ( $0.500\,mol\,dm^{-3}$ ), the amount of acid is lower, potentially making it the limiting reactant. Using the concentration and volume ( $0.500\,mol\,dm^{-3} \times 0.100\,dm^3 = 0.050\,mol$ of $HCl$ ), and given the 1:2 stoichiometry, this would produce $0.025\,mol$ of $CO_2$ .
- In Reaction Two ( $2.00\,mol\,dm^{-3}$ ), there is a higher amount of acid ( $2.00\,mol\,dm^{-3} \times 0.100\,dm^3 = 0.200\,mol$ of $HCl$ ). This is enough to fully react with the $5.00\,g$ ( $\approx 0.050\,mol$ ) of $CaCO_3$ , producing $0.050\,mol$ of $CO_2$ .
- Consequently, Reaction Two will not only be faster than Reaction One but will also produce a greater total volume of carbon dioxide gas because Reaction One does not have sufficient acid to react with all the calcium carbonate.