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When 3.0 moles of carbon monoxide and 1.0 moles of steam were mixed together in a container of fixed volume V, and in the presence of a suitable catalyst, the following chemical equilibrium was established at a temperature of 800 K - Leaving Cert Chemistry - Question 9 - 2020
Question 9
When 3.0 moles of carbon monoxide and 1.0 moles of steam were mixed together in a container of fixed volume V, and in the presence of a suitable catalyst, the follow... show full transcript
Worked Solution & Example Answer:When 3.0 moles of carbon monoxide and 1.0 moles of steam were mixed together in a container of fixed volume V, and in the presence of a suitable catalyst, the following chemical equilibrium was established at a temperature of 800 K - Leaving Cert Chemistry - Question 9 - 2020
Step 1
Explain chemical equilibrium.
Answer
Chemical equilibrium occurs when the concentrations of reactants and products remain constant over time, meaning that the rates of the forward and reverse reactions are equal. This balance between the forward reaction (where reactants are converted into products) and the reverse reaction (where products revert to reactants) results in a dynamic state. The term 'dynamic' reflects that even though the macroscopic properties are stable, molecular activities are continuously occurring.
Step 2
Step 3
Calculate the number of moles of carbon monoxide in the equilibrium mixture at this temperature.
Answer
We denote the initial moles of carbon monoxide (CO) as 3.0 moles and the initial moles of steam (H2O) as 1.0 mole. Let x be the change in moles of carbon monoxide that reacts. The changes in moles will be:
Initial:
- CO: 3.0 - x
- H2O: 1.0 - x
- CO2: 0 + x
- H2: 0 + x
At equilibrium, we express the concentrations in terms of x:
The equilibrium constant is 4.0:
ightarrow 4.0 = \frac{x^2}{(3.0 - x)(1.0 - x)}$$ Solving for x leads to a quadratic equation, which we can factor or use the quadratic formula to find the value. After calculations, we find: - For x = 0.9082, moles of CO = 3.0 - 0.9082 = 2.0918 moles - For x = 4.4305, moles of CO = 3.0 - 4.4305 is not feasible. Thus, the number of moles of carbon monoxide in the equilibrium mixture is approximately 2.1 moles.Step 4
Step 5
Predict the effect, if any, of adding more steam at 800 K to the equilibrium mixture (ii) on the equilibrium yield of hydrogen.
Answer
Adding more steam would shift the equilibrium position to the right (towards the products), increasing the equilibrium yield of hydrogen. This is consistent with Le Chatelier's principle, which states that a system at equilibrium will shift in response to an external change to counteract that change.
Step 6
State and explain the effect on the value of Kc of increasing the equilibrium temperature.
Answer
Increasing the equilibrium temperature will generally decrease the value of Kc for exothermic reactions (like the one considered, which releases heat). According to Le Chatelier's principle, increasing the temperature favors the endothermic direction (the reverse reaction in this case) to absorb the added heat, thus lowering the equilibrium constant.