Photo AI
For which reactions does the value of ΔH° represent both a standard enthalpy change of combustion and a standard enthalpy change of formation? 1 - CIE - A-Level Chemistry - Question 33 - 2018 - Paper 1
Question 33
For which reactions does the value of ΔH° represent both a standard enthalpy change of combustion and a standard enthalpy change of formation? 1. C(s) + O2(g) → CO2(... show full transcript
Worked Solution & Example Answer:For which reactions does the value of ΔH° represent both a standard enthalpy change of combustion and a standard enthalpy change of formation? 1 - CIE - A-Level Chemistry - Question 33 - 2018 - Paper 1
Step 1
1. C(s) + O2(g) → CO2(g)
Answer
This reaction represents the combustion of carbon to form carbon dioxide. It is a standard enthalpy change of combustion. However, it does not represent an enthalpy change of formation, as formation reactions involve the formation of one mole of a compound from its elements in their standard states.
Step 2
2. 2C(s) + O2(g) → 2CO(g)
Answer
This reaction represents the combustion of carbon to form carbon monoxide. It is a standard enthalpy change of combustion but, like the first reaction, it does not qualify as an enthalpy change of formation since it does not yield one mole of a single product.
Step 3
3. CO(g) + rac{1}{2}O2(g) → CO2(g)
Answer
This reaction shows the formation of carbon dioxide from carbon monoxide and oxygen. It is a standard enthalpy change of formation, and does not represent combustion. Therefore, this option meets the criterion of a standard enthalpy change of formation but not of combustion.