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Question

A scientist conducted several experiments, combining different reactants to produce chemical reactions. She recorded the starting temperature of the reactants and ending temperatures of the products for each reaction.

Select the chemical reactions that represent endothermic reactions. Select all that apply.

Table with columns labeled chemical reaction, reactants, products, starting temperature in degrees Celsius, and ending Temperature in degrees Celsius. 1st row: A, calcium carbonate, calcium oxide and carbon dioxide, 23, 15. 2nd row: B, carbon and hydrogen, acetylene, 21, 18. 3rd row: C, methane and oxygen, carbon dioxide and water, 22, 35. 4th row: D, octane and oxygen, water and carbon dioxide, 24, 86

Reaction A

Reaction B

Reaction C

Reaction D

Answer 1

To determine which reactions are endothermic, we need to look at the starting and ending temperatures. In an endothermic reaction, the system absorbs heat from the surroundings, leading to a decrease in temperature of the reactants.

Let's analyze the given reactions:

1. Reaction A: Starting temperature = 23°C, Ending temperature = 15°C.

   • The temperature decreased, indicating it is an endothermic reaction.

2. Reaction B: Starting temperature = 21°C, Ending temperature = 18°C.

   • The temperature decreased, indicating it is an endothermic reaction.

3. Reaction C: Starting temperature = 22°C, Ending temperature = 35°C.

   • The temperature increased, indicating it is an exothermic reaction.

4. Reaction D: Starting temperature = 24°C, Ending temperature = 86°C.

   • The temperature increased, indicating it is an exothermic reaction.

Based on this analysis, the reactions that represent endothermic reactions are:

• Reaction A
• Reaction B