Exothermic & Endothermic Reactions

9.In a bond energy calculation, if the total energy absorbed to break bonds is 500 kJ and the total energy released forming new bonds is 600 kJ, what is the enthalpy change and what type of reaction is it?

10.The decomposition of hydrogen bromide: 2HBr → H₂ + Br₂ has an enthalpy change of +103 kJ. Given bond energies: H–Br = 366 kJ/mol, H–H = 436 kJ/mol, what is the bond energy of Br–Br?

11.Which of the following correctly describes the energy change of the system in an endothermic reaction?

12.A student uses a polystyrene cup instead of a glass beaker in an experiment to measure temperature changes. What is the main reason for using a polystyrene cup?

13.In an experiment, 4 g of solid A is added to 30 cm³ of water and the temperature decreases from 20 °C to 16 °C. Which type of reaction is this?

14.A student adds 4 g of solid B to 30 cm³ of water and observes a temperature rise from 20 °C to 26 °C. What is the temperature change?

15.In an experiment, 4 g of solid D is added to 30 cm³ of water and the temperature rises from 19 °C to 31 °C. If the experiment is repeated using 60 cm³ of water and the same mass of solid D, what would be the expected temperature change?

16.A student adds 1 g of powdered sodium thiosulphate to 20 cm³ of water and the temperature changes. The experiment is repeated with 2 g, 3 g, 4 g, and 5 g. The results show a linear increase in temperature with mass. What temperature would be expected for 3.5 g?

17.In a neutralisation experiment, 25 cm³ of sodium hydroxide solution is reacted with varying volumes of hydrochloric acid. The temperature change is plotted against acid volume. Two straight lines are drawn through the points; they intersect at 10 cm³ of acid. What volume of acid is needed to neutralise the sodium hydroxide?

18.Why is a polystyrene cup used instead of a glass beaker in temperature change experiments?

19.In a reaction pathway diagram for an exothermic reaction, which statement is correct?

20.Given the bond energies: H–H = 436 kJ/mol, I–I = 151 kJ/mol, H–I = 295 kJ/mol, what is the enthalpy change for the reaction H₂ + I₂ → 2HI?

21.What is the term for the minimum amount of energy required for a successful collision between reactant particles?

22.In an experiment, sodium thiosulphate is powdered before dissolving in water. What is the reason for this?

23.In an experiment, 30 cm³ of water is placed in a polystyrene cup and its initial temperature is measured. 4 g of solid B is added, stirred, and the final temperature is recorded. The temperature increases by 6 °C. Which of the following is the most likely reason for using a polystyrene cup?

24.A student adds 4 g of solid D to 30 cm³ of water and observes a temperature rise from 19 °C to 31 °C. The experiment is repeated using 60 cm³ of water instead of 30 cm³, keeping the mass of solid D the same. What would be the expected temperature change?

25.In an experiment, 1 g of powdered sodium thiosulphate is added to 20 cm³ of water and the temperature decreases. The experiment is repeated with 2 g, 3 g, 4 g, and 5 g. The results are plotted on a graph of temperature against mass of sodium thiosulphate. Which of the following is the most likely shape of the graph?

26.In a neutralisation experiment, 25 cm³ of sodium hydroxide solution is reacted with varying volumes of hydrochloric acid. The temperature change is plotted against volume of acid added. Two straight lines are drawn through the points and they cross. What does the crossing point represent?

27.In a reaction pathway diagram, the energy of the reactants is higher than the energy of the products. Which of the following is correct?

28.Given the bond energies: C–H = 413 kJ/mol, O=O = 498 kJ/mol, C=O = 805 kJ/mol, O–H = 464 kJ/mol. For the combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O. What is the enthalpy change of the reaction?

29.A student investigates the reaction between sodium hydroxide and hydrochloric acid. Both solutions are left to stand in the laboratory for about 30 minutes before the experiment. Why is this done?

30.Hydrogen bromide decomposes: 2HBr → H₂ + Br₂. The enthalpy change is +103 kJ. Given bond energies: H–Br = 366 kJ/mol, H–H = 436 kJ/mol. What is the bond energy of Br–Br?

31.In an experiment to measure temperature changes during a reaction, a student uses a thermometer to stir the mixture. What is the most likely effect of this?

32.A reaction pathway diagram shows the activation energy (Eₐ) and the enthalpy change (ΔH). Which of the following statements is correct?

33.Which of the following is an exothermic reaction?

34.In an exothermic reaction, thermal energy is transferred from the _____ to the _____.

35.Which of the following is an endothermic process?

36.In a reaction pathway diagram for an exothermic reaction, the energy of the products is _____ the energy of the reactants.

37.What is the enthalpy change (ΔH) for an exothermic reaction?

38.The reaction 2HBr → H₂ + Br₂ has an enthalpy change of +103 kJ. Given bond energies: H–Br = 366 kJ/mol, H–H = 436 kJ/mol, what is the bond energy of Br–Br?

39.In a bond energy calculation, if the total energy absorbed to break bonds is 500 kJ and the total energy released forming new bonds is 600 kJ, what is the enthalpy change and the type of reaction?

40.A student adds 4 g of solid to 30 cm³ of water and observes a temperature decrease. Which type of reaction is this?