CaCO3(s) CaO(s) + CO2(g) ΔH = 177.8 kJ
Use your understanding of enthalpy changes to determine the relative stabilities of the reactants and products.
The positive value of ΔH (177.8 kJ) indicates that the reaction is endothermic, meaning energy is absorbed from the surroundings during the reaction. This suggests that the products are less stable than the reactants.
In this case, the reactant is CaCO3 (solid calcium carbonate) and the products are CaO (solid calcium oxide) and CO2 (gaseous carbon dioxide). The conversion of a solid to another solid does not involve a change in state, so the stability can be inferred from the chemical properties of the substances.
Calcium carbonate is a relatively stable compound, whereas calcium oxide is a more reactive compound. This is reflected in their reactivities with water - calcium carbonate does not react with water, while calcium oxide vigorously reacts with water to form calcium hydroxide.
Therefore, it can be inferred that CaCO3 (the reactant) is more stable than CaO (the product). Similarly, carbon dioxide is a relatively stable compound in the gas phase, while calcium oxide is more reactive, suggesting that CO2 (the product) is more stable than CaO.
Enthalpy change (ΔH) is a measure of the heat transferred during a chemical reaction. A positive ΔH value indicates that the reaction is endothermic, meaning heat is absorbed from the surroundings. Conversely, a negative ΔH value indicates that the reaction is exothermic, meaning heat is released to the surroundings.
In the given reaction, the ΔH value is 177.8 kJ, which is positive. This indicates that the reaction is endothermic and requires heat to proceed.
Based on this information, we can say that the reactant, CaCO3(s) (calcium carbonate), is less stable than the products, CaO(s) (calcium oxide) and CO2(g) (carbon dioxide). This is because the reaction absorbs heat energy from the surroundings to form the products.
Therefore, the products, CaO(s) and CO2(g), are more stable than the reactant, CaCO3(s).