iGCSE Chemistry (0620) Core:5.1 Exothermic and endothermic reactions: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The more exothermic a reaction is, the more heat energy it dumps into the surroundings, raising the temperature. On a reaction pathway diagram, an exothermic reaction has the products sitting lower in energy than the reactants. The bigger the energy drop from reactants to products, the more heat is given out. Diagram C shows the largest vertical gap downwards, which represents the biggest overall transfer of thermal energy to the surroundings, so it will cause the largest temperature increase.
▶️ Answer/Explanation
Detailed solution:
Statement 1 is wrong because endothermic reactions take in energy from the surroundings, making the surroundings cooler. Statement 2 is wrong because exothermic reactions transfer energy out to the surroundings; it is endothermic reactions that take in energy. Statement 3 is correct: in an exothermic reaction, the products end up with less energy than the reactants started with, so on the energy level diagram, the products are drawn lower down than the reactants. Only statement 3 is correct.
▶️ Answer/Explanation
Detailed solution:
A temperature decrease means heat is absorbed from the surroundings, so the process is endothermic. Since the ammonium nitrate is simply recovered by evaporating water, it has dissolved, not undergone a chemical reaction. If it had reacted, you wouldn’t get the original substance back by just removing water. So, it’s a dissolving process that is endothermic.