Explain the term activation energy (Ea) - Leaving Cert Chemistry - Question c - 2022
Question c
Explain the term activation energy (Ea).
The reaction profile diagram for the reaction X → Y, with and without catalyst C, is shown below.
What is the value of Ea ... show full transcript
Worked Solution & Example Answer:Explain the term activation energy (Ea) - Leaving Cert Chemistry - Question c - 2022
Step 1
Explain the term activation energy (Ea).
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Answer
The activation energy (Ea) is defined as the minimum combined energy of colliding particles (or molecules) required for a chemical reaction to occur. It represents the energy barrier that must be overcome for the reactants to be transformed into products. A mention of the necessity for effective collisions to happen is also implicit in this definition.
Step 2
What is the value of Ea for the reaction X → Y without the catalyst?
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Answer
The value of Ea for the reaction X → Y without a catalyst is 100 kJ mol⁻¹.
Step 3
By how much does catalyst C lower the value of Ea for the reaction?
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The catalyst C lowers the value of Ea for the reaction by 40 kJ mol⁻¹.
Step 4
What is the value of ΔH for the reverse reaction Y → X?
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Answer
The value of ΔH for the reverse reaction Y → X is -30 kJ mol⁻¹.
Step 5
Explain the underlined term.
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Answer
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It provides an alternative reaction pathway with a lower activation energy, facilitating the conversion of reactants to products.
Step 6
Describe the mechanism by which the catalyst increases the rate of this reaction.
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Answer
In this reaction, hydrogen and oxygen gases are adsorbed on the surface of the catalyst (e.g., platinum). The weak interactions between the reactants and the catalyst enhance the probability of collisions. This higher concentration of reactants near the active sites on the catalyst allows for better-oriented collisions, lowering the activation energy. Consequently, reactants undergo bond breaking and forming more easily. Ultimately, the product, water, is formed and desorbs from the catalyst surface.
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