What is revealed in the reaction $Ca ( OH )_2(s) \rightarrow Ca ^{2+}(a q)+2 OH ^{-}(a q)$. $\Delta H=-16.71$?
A. The reaction produces heat.
B. Heat is one of the reactants.
C. The reaction is endothermic.
D. The reaction occurs slowly.
Answer (1)
A negative Δ H indicates an exothermic reaction.
Exothermic reactions release heat.
The given reaction has a negative Δ H value.
Therefore, the reaction produces heat, and the answer is A. A
Explanation
Understanding the Problem The problem states that the reaction C a ( O H ) 2 ( s ) i g h t ha r p oo n C a 2 + ( a q ) + 2 O H − ( a q ) has a Δ H = − 16.71 . We need to determine what this negative value of Δ H tells us about the reaction.
Recalling Enthalpy and Exothermic Reactions Recall that Δ H represents the change in enthalpy for a reaction. A negative Δ H indicates that the reaction is exothermic, meaning it releases heat. An exothermic reaction produces heat as a product.
Concluding the Reaction Type Therefore, the reaction C a ( O H ) 2 ( s ) i g h t ha r p oo n C a 2 + ( a q ) + 2 O H − ( a q ) produces heat.
Identifying the Correct Answer The correct answer is A. The reaction produces heat.
Examples
In real life, understanding exothermic reactions is crucial in various applications. For example, the dissolution of calcium chloride ( C a C l 2 ) in water is an exothermic process, releasing heat. This property is utilized in self-heating hand warmers, where the chemical reaction provides warmth during cold weather. Similarly, the combustion of fuels like propane or natural gas in furnaces is an exothermic reaction that heats homes and buildings.
