Multiple Choice
When iron metal is mixed with hydrochloric acid in a coffee cup calorimeter, the temperature rises from 25.2°C to a final temperature. What type of reaction is occurring?
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8. Thermochemistry
Endothermic & Exothermic Reactions
Multiple Choice
Which of the following reactions is exothermic?
A
Photosynthesis
B
Evaporation of water
C
Melting of ice
D
Combustion of methane
Verified step by step guidance1
Understand the concept of exothermic reactions: Exothermic reactions are chemical reactions that release energy, usually in the form of heat, to the surroundings. This is often observed as an increase in temperature of the surroundings.
Identify the nature of each given reaction: Photosynthesis, evaporation of water, and melting of ice are processes that absorb energy from the surroundings, making them endothermic. Combustion of methane, however, releases energy, making it exothermic.
Examine the combustion of methane: The chemical equation for the combustion of methane is \( \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} \). This reaction releases energy as heat and light, indicating it is exothermic.
Compare the energy changes: In exothermic reactions like the combustion of methane, the energy released from forming the products is greater than the energy required to break the reactants' bonds.
Conclude that the combustion of methane is exothermic: Based on the energy release and the nature of the reaction, combustion of methane is the correct answer as an exothermic reaction.
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