Question

Two chemicals are combined in a beaker and react. What data would provide the best evidence for determining if the reaction absorbed or released thermal energy?

Group of answer choices
1. Whether or not light and sound were produced during the reaction
2. The temperature inside the beaker before and after the reaction
3. How long it took for the reaction to take place once the chemicals combined
4. The masses of the substances before and after the reaction"

Answer 1

To determine if a chemical reaction absorbed or released thermal energy, the temperature change observed in a calorimetry experiment is the best indicator. Exothermic reactions increase the temperature, while endothermic reactions decrease it. Mass changes do not indicate the energy profile of the reaction.

Step-by-step explanation:

The best evidence for determining if a chemical reaction absorbed or released thermal energy would be the data of the temperature inside the beaker before and after the reaction. If the reaction is exothermic, it means that thermal energy is released into the surroundings, causing the temperature of the surroundings to increase. On the other hand, an endothermic reaction absorbs thermal energy, resulting in a decrease in temperature. Since measuring the masses of substances doesn't directly reflect energy changes, it's less useful in determining whether the reaction absorbed or released energy.

Through calorimetry, we can measure the temperature change and, using the heat capacity of the substances involved, calculate the amount of heat absorbed or released. This technique pinpoints changes in enthalpy (ΔH), which corresponds to the thermal energy change due to the reaction at constant pressure.