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5 marksPrinciples of Chemical Equilibrium

CAPE Chemistry Unit 1 · 2006 · Paper 2 · Question 4(a)(iii)

Iodine gas is purple and hydrogen iodide gas is colourless. Hydrogen and iodine, in the gaseous state, react according to the equation: H2(g) + I2(g) <=> 2 HI(g)

Describe and explain, with reference to changes in colour, the observations made when hydrogen gas is reacted with iodine gas at constant temperature until equilibrium is achieved.

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Other parts of this question

  1. 4(a)(i)Describe the features of a chemical system in a state of dynamic equilibrium.[4 marks]
  2. 4(a)(ii)Define the term 'equilibrium constant'.[1 mark]
  3. 4(a)(iv)a)Use the information in Table 3 and the equation in (a) (iii) above to calculate the number of moles of hydrogen reacting.[3 marks]
  4. 4(a)(iv)b)Complete the table by inserting the equilibrium concentrations of I2 and HI.[3 marks]
  5. 4(a)(v)Write an equation for Kp for the reaction in (iii) above.[2 marks]
  6. 4(b)(i)a)Write an expression for EACH of the following terms: Ka[3 marks]
  7. 4(b)(i)b)Write an expression for EACH of the following terms: pKa[3 marks]
  8. 4(b)(i)c)Write an expression for EACH of the following terms: pH[3 marks]
  9. 4(b)(ii)Given that Ka for acid HP is 3.0 x 10-5 mol dm-³, predict the relative size of Ka for a stronger acid HQ. Explain your reasoning.[2 marks]

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