IB CHEMISTRY

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Reactivity 1.1 Exam Practice

Section A: Multiple Choice

1. Which statement is correct for an endothermic reaction?

A. The enthalpy of reactants is higher than products.
B. The temperature of the surroundings decreases. (Correct)
C. The enthalpy change (ΔH\Delta H) is negative.
D. Bonds are formed only.

2. A block of metal (c=0.5 J g−1 K−1c = 0.5 \text{ J g}^{-1} \text{ K}^{-1}) of mass 10g increases temp by 10K. What is qq?

A. 50 J (Correct)
B. 5 J
C. 100 J
D. 0.5 J

Section B: Structured Questions

Q1: Calorimetry Experiment [4 marks]

0.10 moles of Magnesium is reacted with excess HCl in a calorimeter containing 100g of water. The temperature rises from 20.0°C to 45.0°C.

  1. Calculate the heat energy (qq) absorbed by the water. (c=4.18c = 4.18) [1]
  2. Calculate the Molar Enthalpy Change (ΔH\Delta H) for the reaction in kJ mol−1\text{kJ mol}^{-1}. [2]
  3. State if the reaction is Exothermic or Endothermic. [1]

Examiner's Markscheme

1. q=100×4.18×(45−20)=10450Jq = 100 \times 4.18 \times (45-20) = 10450 \text{J}

2. ΔH=−q/n=−10450/0.10=−104,500J\Delta H = -q/n = -10450 / 0.10 = -104,500 \text{J}. Convert to kJ: -105 kJ/mol.

3. Exothermic (Temp increased/Negative sign).