Worksheet Chapter 5: Thermochemistry

1. True or False: Instant hot packs use an endothermic chemical reaction to generate thermal energy for warming hands.

2. A student dissolves $10 g$ of sodium hydroxide ($NaOH$) in $100 cm³$ of water in a polystyrene cup. The initial temperature of water is $28^\circC$ and the maximum temperature reached is $42^\circC$. Identify the type of reaction, calculate the temperature change, and explain the heat flow involved.

3. Fill in the blank: A chemical reaction that releases heat energy to the surroundings, causing the temperature to rise, is called an ____________ reaction.

4. Which of the following substances undergoes an endothermic reaction when dissolved in water?

5. True or False: During an endothermic reaction, the final energy level of the products is lower than the initial energy level of the reactants.

6. Give two differences between an exothermic reaction and an endothermic reaction in terms of heat change and temperature of the surroundings.

7. Compare cellular respiration and photosynthesis in terms of thermochemistry, explaining their heat energy changes and environmental significance.

8. Explain how an instant cold pack works when squeezed to relieve pain from a sports injury.

9. An investigation was carried out to study two chemical reactions in polystyrene cups: Reaction X: $50 cm³$ Hydrochloric acid + $50 cm³$ Sodium hydroxide solution ($27^\circC arrow 35^\circC$) Reaction Y: $50 cm³$ Ethanoic acid + $5 g$ Sodium hydrogen carbonate ($27^\circC arrow 20^\circC$) (a) Classify Reaction X and Reaction Y as exothermic or endothermic. (b) Compare the relative energy levels of reactants and products for both reactions. (c) Why are polystyrene cups used instead of glass beakers in this experiment?

10. State the type of reaction (Exothermic or Endothermic) for each of the following processes: (a) Burning of magnesium ribbon in air (b) Photosynthesis in green plants