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
111–117 of 117
Question 111
2 marks · Hard
Answer and see the solution →The following reaction occurs:
Bond energies (in kJ/mol):
Bond Bond energy / kJ mol^{-1} H–H 436 F–F 158 H–F 565 Calculate the enthalpy change (ΔH) for the reaction using the bond energies given.
Question 112
5 marks · Hard
Answer and see the solution →Chloroethane can be made by reacting ethene with hydrogen chloride:
Bond energies (kJ/mol) Bond Bond energy / kJ mol^{-1} C=C 612 C–C 348 C–H 413 H–Cl 432 C–Cl 338 (a)[2 marks]Write down all the bonds broken and all the bonds formed in this reaction.
(b)[3 marks]Calculate the enthalpy change (ΔH), in kJ/mol, for the reaction using the bond energies provided. Show your working and give your answer to the nearest kJ/mol.
Question 113
2 marks · Hard
Answer and see the solution →A student calculates the enthalpy change for the following reaction using average bond energies:
Bond energies (kJ/mol):
Bond Bond energy / kJ mol^{-1} Cl–Cl 243 H–S 363 H–Cl 432 State the total energy required to break all the bonds in the reactants, and the total energy released when new bonds form in the products. Show your calculations.
Question 114
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 115
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 116
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.
Question 117
5 marks · Easy
Answer and see the solution →Magnesium reacts with dilute hydrochloric acid in a reaction described below:
The reaction is exothermic. An energy profile for this reaction is shown below, but the axes and key features have not been labelled.
(a)Incomplete energy profile diagram for: \ce{Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)} (i)[2 marks]On the diagram, clearly label: - the correct position of the reactants and products; - the activation energy; - the enthalpy change (ΔH), with an arrow showing its direction.
(b)In a second experiment, a student dissolves ammonium chloride (NH₄Cl) in water. She uses 50.0 g of water at 24.0°C. After the salt dissolves, the final temperature is 19.7°C. The specific heat capacity, c, of water is 4.18 J/(g°C).
Calculate the heat energy change (Q) for the dissolving process. State if the reaction is exothermic or endothermic, and explain your answer.
(i)[2 marks]Calculate the heat energy change, Q, for this process. Give the unit.
(ii)[1 mark]State if this process is exothermic or endothermic and explain your answer.