Thermochemistry

Free sample questions

Thermochemistry — sample Science questions with answers

1. Question 1

   Which of the following processes is an exothermic reaction?

   • ACombustion of magnesium in oxygen
   • BPhotosynthesis
   • CDissolution of ammonium chloride in water
   • DDecomposition of calcium carbonate

   Answer: A. Combustion of magnesium in oxygen

   Combustion of magnesium in oxygen releases heat, therefore it is an exothermic reaction. Photosynthesis, dissolution of ammonium chloride, and decomposition of calcium carbonate require heat (endothermic).

2. Question 2

   In an exothermic reaction, the temperature of the reaction mixture will ________.

   • Adecrease
   • Bincrease
   • Cremain unchanged
   • Dincrease then decrease

   Answer: B. increase

   An exothermic reaction releases heat to the surroundings, causing the temperature of the mixture to increase.

3. Question 3

   An energy level diagram shows that the energy of reactants is higher than the energy of products. What type of reaction is this?

   • AExothermic
   • BEndothermic
   • CNeutralisation
   • DCombustion

   Answer: A. Exothermic

   When the energy of reactants is higher than that of products, energy is released to the surroundings, indicating an exothermic reaction.

4. Question 4

   What temperature change occurs during the dissolution of solid sodium hydroxide in water?

   • ATemperature increases
   • BTemperature decreases
   • CTemperature does not change
   • DTemperature increases then decreases sharply

   Answer: A. Temperature increases

   Dissolution of sodium hydroxide in water is exothermic, releasing heat and causing the solution temperature to increase.

5. Question 5

   In the reaction $\text{Mg}+\text{HCl}\to {\text{MgCl}}_2+{\text{H}}_2$, the temperature of the mixture increases. What is the value of $\Delta H$ for this reaction?

   • A$\Delta H$ positive
   • B$\Delta H$ negative
   • C$\Delta H=0$
   • D$\Delta H$ cannot be determined

   Answer: B. $\Delta H$ negative

   The temperature increase indicates an exothermic reaction, which has a negative $\Delta H$ (heat is released).