Chemistry · May / June 2024 · Paper 41 · Question 4
0620
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Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible. 2HI(g) I2(g) + H2(g) colourless gas purple gas colourless gas Fig. 4.1 shows a gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases. The gas syringe is sealed and the mixture is heated to 300 °C. The mixture of gases reaches equilibrium and is purple. end sealed plunger equilibrium mixture of hydrogen iodide, iodine and hydrogen Fig. 4.1
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4(a)[2]
M1 The rate of forward reaction equals the rate of the reverse reaction(1)
M2 concentrations of reactants and products are no longer changing(1)
4(b)(i)[1]
same number of gas moles on both sides of the equilibrium
OR
same number of gas molecules on both sides of the equilibrium
4(b)(ii)[1]
iodine particles or molecules (forced) closer together
OR
same number of iodine particles or molecules in a smaller volume
4(c)[1]
endothermic
4(d)[2]
M1 –1 (1)
M2 zero (1)
4(e)(i)[1]
copper
4(e)(ii)[1]
no effect
4(e)(iii)[1]
(activation energy is) lower
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