Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Energetics
117 practice questions
Topics covered
- Exothermic reactions19 practice questions
- Endothermic reactions19 practice questions
- Measuring enthalpy changes of reactions19 practice questions
- Calorimetry experiments for determining the enthalpy changes of reactions18 practice questions
- Why do reactions either give out or absorb heat?19 practice questions
- Calculation of enthalpy changes of reaction using bond energies19 practice questions
Practice questions
41–50 of 51 · Easy
Question 41
3 marks · Easy
Answer and see the solution →(a)[1 mark]State whether bond breaking is exothermic or endothermic.
(b)[1 mark]State whether bond making is exothermic or endothermic.
(c)[1 mark]Explain your answer to part b.
Question 42
2 marks · Easy
Answer and see the solution →Calculate the enthalpy change (ΔH) for the following reaction using the bond energies given below: Bond energies (kJ/mol):
Bond Bond energy / kJ mol^{-1} H–H 436 Br–Br 193 H–Br 366 Question 43
2 marks · Easy
Answer and see the solution →Explain why a reaction is exothermic in terms of bond energies.
Question 44
3 marks · Easy
Answer and see the solution →The table below gives bond energies (kJ/mol):
Bond Bond energy / kJ mol^{-1} C–C 151 C–H 413 H–H 436 Use these values to answer the following about the reaction:
(a)[1 mark]List all the bonds broken and all formed in this reaction.
(b)[1 mark]Calculate the total energy required to break bonds in the reactant.
(c)[1 mark]Calculate the enthalpy change (ΔH) for the reaction.
Question 45
1 mark · Easy
Answer and see the solution →State the unit in which bond energy is measured.
Question 46
3 marks · Easy
Answer and see the solution →Bond energies are given below:
Bond Bond energy / kJ mol^{-1} N≡N 946 H–H 436 N–H 388 Use the bond energies to answer the following about the reaction:
(a)[1 mark]Calculate the total energy needed to break all bonds in the reactants.
(b)[1 mark]Calculate the total energy released by forming all bonds in the products.
(c)[1 mark]Determine the enthalpy change (ΔH) for the reaction.
Question 47
2 marks · Easy
Answer and see the solution →The reaction below occurs: Bond energies (kJ/mol): HI: 299, H–H: 436, I–I: 151 Calculate the enthalpy change (ΔH) for the reaction.
Question 48
5 marks · Easy
Answer and see the solution →A student investigates the energy change when potassium nitrate dissolves in water.
(a)[1 mark]State whether this process is exothermic or endothermic.
(b)[2 marks]The student adds 5.0 g of potassium nitrate ( KNO_3 ) to 50.0 g of water in a polystyrene cup. The temperature drops from 20.0°C to 15.5°C. Calculate the heat energy change (Q) for the water. (Specific heat capacity of water = 4.18 J/g°C)
(c)[1 mark]Calculate the number of moles of potassium nitrate dissolved. (M_r of KNO_3 = 101)
(d)[1 mark]Calculate the molar enthalpy change (ΔH) for this process in kJ/mol. Give your answer to 2 significant figures.
Question 49
5 marks · Easy
Answer and see the solution →A student adds 2.00 g of magnesium powder to 50.0 cm³ of dilute sulfuric acid in a polystyrene cup. The temperature of the mixture increases from 22.0°C to 27.4°C.
(a)[2 marks]State whether the reaction between magnesium and sulfuric acid is exothermic or endothermic. Explain your answer using the temperature change.
(b)[2 marks]Use your answer from (a). Calculate the heat energy change, Q, in joules for this reaction. [Assume the specific heat capacity of the solution is 4.18 J/g°C and its mass is 50.0 g. Use Q = mcΔT.]
(c)[1 mark]Is the value of Q calculated in part (b) positive or negative for this reaction? Suggest a reason for the sign based on your answer to part (a).
Question 50
5 marks · Easy
Answer and see the solution →(a)[2 marks]The equation below represents the reaction between calcium oxide and water:
Draw an energy profile diagram for the reaction above, clearly labelling the reactants, products, and the direction of energy change. Indicate whether the reaction is exothermic or endothermic.
(b)[2 marks]A student adds calcium oxide to 100.0 g of water in an insulated cup. The temperature rises from 20.0 C to 32.5 C. Calculate the heat energy released to the water. (Assume the specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹.)
(c)[1 mark]Another experiment involves dissolving ammonium nitrate in water, which lowers the temperature of the same mass of water by the same number of degrees as your answer in (b). Explain, in terms of heat transfer, whether this second reaction is exothermic or endothermic.