Question detail
Define standard enthalpy change of formation and provide an example.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Energetics
Question
Define standard enthalpy change of formation and provide an example.
Answer
The standard enthalpy change of formation is the enthalpy change when one mole of a compound is formed from its elements in their standard states. For example, the formation of water (H2O) from hydrogen (H2) and oxygen (O2) is represented as: H2(g) + 1/2 O2(g) → H2O(l).
Explanation
This answer is strong because it clearly defines the concept of standard enthalpy change of formation and provides a relevant example with a balanced equation. The question tests the student's understanding of enthalpy changes in chemical reactions.
Common mistake
Confusing Enthalpy Changes
Students often confuse standard enthalpy changes for formation with those for combustion, leading to incorrect calculations.
To fix this, remember that the standard enthalpy change of formation refers to the enthalpy change when one mole of a compound is formed from its elements in their standard states, while the standard enthalpy change of combustion is the enthalpy change when one mole of a substance is completely burned in oxygen. Use the correct formula for each type of enthalpy change and ensure you know the definitions clearly.
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