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Consider the following energy profile diagram for a reaction represented by the equation X + Y → Z - VCE - SSCE Chemistry - Question 12 - 2012 - Paper 1
Question 12
Consider the following energy profile diagram for a reaction represented by the equation X + Y → Z. Which one of the following provides the correct values of the ac... show full transcript
Worked Solution & Example Answer:Consider the following energy profile diagram for a reaction represented by the equation X + Y → Z - VCE - SSCE Chemistry - Question 12 - 2012 - Paper 1
Step 1
Activation energy (kJ mol⁻¹)
Answer
The activation energy for this reaction can be determined from the energy difference between the reactants (X + Y) and the peak of the energy profile, which indicates the transition state. Reading from the diagram, the energy of the reactants is approximately 25 kJ mol⁻¹, and the peak (transition state) is around 100 kJ mol⁻¹. Therefore, the activation energy is:
Step 2
Enthalpy (kJ mol⁻¹)
Answer
The enthalpy change for the reaction is the difference in energy between the reactants and products. From the diagram, the products Z appear to return to the energy level of approximately 75 kJ mol⁻¹ after the peak transition state. Hence, the enthalpy change can be calculated as:
However, in this case, if the energy of products is higher than the energy of reactants, then adjust accordingly for the correct understanding.
Based on the options provided, and given the values correlate well to Option A, the answers should be:
- Activation Energy = +75 kJ mol⁻¹
- Enthalpy = +100 kJ mol⁻¹