In the decomposition of CaCO3 a gas is produced: CaCO3 (s) → CaO (s) + CO2 (g). Predict the change in entropy for this reaction.
The predicted change in entropy would be:
a. ΔS < 0
b. ΔS = 0
c. ΔS > 0
d. Enthalpy required
My answer is c but could someone check this. Thanks
That is correct. Reactions occur spontaneously if dS is +. Gases have more entropy than solids; therefore, this reaction will have a + dS.
To predict the change in entropy for the decomposition of CaCO3, we can consider the number of molecules involved before and after the reaction.
Before the reaction:
1 molecule of CaCO3 (solid)
After the reaction:
1 molecule of CaO (solid)
1 molecule of CO2 (gas)
Since there is an increase in the number of molecules and the system goes from having one solid to having one solid and one gas, we can conclude that there is an increase in disorder or randomness.
An increase in disorder corresponds to an increase in entropy (ΔS > 0). Therefore, your answer of c. ΔS > 0 is correct.
To predict the change in entropy for the given reaction, we need to consider the states of the reactants and products. Entropy (ΔS) is a measure of disorder or randomness in a system, so we need to analyze the number of particles and the phase changes involved.
In the given reaction:
CaCO3 (s) → CaO (s) + CO2 (g)
1. The reactant, CaCO3, is a solid, which means its particles are packed in a organized and fixed arrangement. This implies a low entropy value.
2. The product, CaO, is also a solid, so its entropy is expected to be similar to that of CaCO3.
3. The product, CO2, is a gas, which means its particles are more spread out and have more freedom of movement. This implies a higher entropy value compared to the solids.
Based on these considerations, the reaction involves the conversion of a solid reactant into a solid product and a gas product. Since the gas product has higher entropy than the solid reactant, we can conclude that the reaction will lead to an overall increase in entropy.
Therefore, the correct answer is c. ΔS > 0.
Note: Entropy change is related to enthalpy change (ΔH) through the equation ΔG = ΔH - TΔS, but in this question, we are only asked to predict the change in entropy and not the enthalpy required.