Which method do scientists commonly use to determine whether a chemical reaction is endothermic or exothermic?

• A. By measuring the temperature change of the surroundings during the reaction
• B. By observing the color change of the reactants
• C. By measuring the pressure of the system before and after the reaction
• D. By calculating the atomic mass of the products

Answer: (A)

Verified step by step guidance

1. Understand the definitions: An exothermic reaction releases heat to the surroundings, causing the temperature of the surroundings to increase, while an endothermic reaction absorbs heat, causing the temperature of the surroundings to decrease.
2. Recognize that the key to determining whether a reaction is endothermic or exothermic is to observe the heat flow between the system (the reaction) and its surroundings.
3. Note that measuring the temperature change of the surroundings is a direct way to detect heat flow: if the surroundings get warmer, the reaction is exothermic; if they get cooler, the reaction is endothermic.
4. Consider why other options are less effective: color changes may occur but do not directly indicate heat flow; pressure changes relate to gas volume but not heat exchange; atomic mass calculations do not provide information about heat transfer.
5. Conclude that the most common and practical method scientists use is to measure the temperature change of the surroundings during the reaction to determine if it is endothermic or exothermic.