What is revealed in the reaction $Ca ( OH )_2(s) \rightarrow Ca ^{2+}(a q)+$ $2 OH ^{-}(a q)$, $\Delta H =-16.71 ?$
A. Heat is one of the reactants.
B. The reaction occurs slowly.
C. The reaction is endothermic.
D. The reaction produces heat.
Answer (2)
The reaction C a ( O H ) 2 ( s ) r i g h t a rro wC a 2 + ( a q ) + 2 O H − ( a q ) has an enthalpy change of Δ H = − 16.71 .
A negative Δ H indicates that the reaction is exothermic.
Exothermic reactions release heat.
Therefore, the reaction produces heat, and the answer is D .
Explanation
Analyzing the Reaction The given reaction is: C a ( O H ) 2 ( s ) r i g h t a rro wC a 2 + ( a q ) + 2 O H − ( a q ) The enthalpy change for this reaction is Δ H = − 16.71 . We need to determine what this information reveals about the reaction.
Determining the Nature of the Reaction The enthalpy change, Δ H , is negative ( Δ H = − 16.71 ). This indicates that the reaction is exothermic. Exothermic reactions release heat into the surroundings.
Concluding the Reaction Type Since the reaction releases heat, heat is a product of the reaction, not a reactant. Therefore, the reaction produces heat.
Final Answer Based on the analysis, the correct answer is: D. The reaction produces heat.
Examples
Understanding whether a reaction is exothermic or endothermic is crucial in many real-world applications. For example, in designing hand warmers, an exothermic reaction is used to release heat. Conversely, endothermic reactions are used in cooling packs to absorb heat. In construction, the exothermic nature of concrete curing needs to be managed to prevent cracking. In cooking, understanding exothermic and endothermic processes helps in controlling cooking temperatures and ensuring food safety.
The reaction C a ( O H ) 2 ( s ) → C a 2 + ( a q ) + 2 O H − ( a q ) has a negative enthalpy change of Δ H = − 16.71 , indicating it is exothermic and produces heat. Therefore, the correct answer is D. The reaction produces heat.
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