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State Le Chatelier's principle - Leaving Cert Chemistry - Question a - 2003
Question a
State Le Chatelier's principle. A gaseous mixture of hydrogen, iodine and hydrogen iodide form an equilibrium according to the following equation. H₂(g) + I₂(g) ⇌ ... show full transcript
Worked Solution & Example Answer:State Le Chatelier's principle - Leaving Cert Chemistry - Question a - 2003
Step 1
State Le Chatelier's principle
Answer
Le Chatelier's principle states that if a system at equilibrium is subjected to a change in conditions (such as concentration, temperature, or pressure), the equilibrium will shift in a direction that counteracts the imposed change, thereby minimizing the effect of the stress applied.
Step 2
Write an expression for the equilibrium constant, Kc, for this system
Answer
The expression for the equilibrium constant, Kc, for the reaction
is given by:
K_c = rac{[HI]^2}{[H₂][I₂]}
where [HI], [H₂], and [I₂] are the molar concentrations of hydrogen iodide, hydrogen, and iodine at equilibrium, respectively.
Step 3
The value of the equilibrium constant, Kc, for this reaction is 50 at 721 K. If 2 moles of hydrogen iodide gas were introduced into a sealed vessel at this temperature calculate the amount of hydrogen iodide gas present when equilibrium is reached.
Answer
Let the initial concentration of hydrogen iodide, [HI], be calculated as follows:
Given that the volume of the vessel is not specified, we can use moles directly. Initially, we have:
- 0 moles of H₂
- 0 moles of I₂
- 2 moles of HI
Using the equilibrium expression, we can define: Let x be the amount of HI that dissociates:
The change in moles at equilibrium will be:
- H₂: 0 + x
- I₂: 0 + x
- HI: 2 - 2x
From the equilibrium constant expression:
K_c = rac{(2 - 2x)^2}{(x)(x)}
Substituting in the value of Kc:
50 = rac{(2 - 2x)^2}{x^2}
Rearranging gives the equation:
Now, expanding and solving this quadratic equation will provide the value of x. After obtaining x, the final concentration of HI can be calculated as:
Calculating for Kc = 50 results in:
- When x is solved, you will find, for example, that x = 0.44, leading to: .