Increasing the pressure has NO effect on the position of the equilibrium H2 + I2 gives 2HI because
Correct answer: C. the number of moles of gas is the same on both sides
- A. the reaction is exothermic
- B. hydrogen iodide is a gas
- C. the number of moles of gas is the same on both sides
- D. the reaction has no catalyst
Explanation
Pressure changes shift an equilibrium only when the two sides differ in the number of gas molecules, and here there are two moles on each side, so neither direction relieves the stress. The rate of reaching equilibrium does rise with pressure, but the position stays put. Temperature changes will still shift this equilibrium, since the two directions differ in enthalpy.
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About Le Chatelier's Principle
Le Chatelier's principle predicts how an equilibrium responds when concentration, pressure or temperature changes. Questions apply it to reversible reactions, identify the direction of shift and distinguish genuine equilibrium changes from the effect of a catalyst, which changes the rate of reaching equilibrium but not its position.
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