Standard Heats of Formation Worksheet
Explore standard heats of formation, enthalpy changes, and Hess's Law with this comprehensive worksheet for Grade 11 Chemistry.
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Standard Heats of Formation
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Read each question carefully and provide your best answer. Use the provided space for calculations and explanations.
1. Which of the following statements best defines the standard enthalpy of formation (ΔH°f)?
The enthalpy change when one mole of a compound is formed from its elements in their standard states.
The enthalpy change when any reaction occurs at standard conditions.
The energy required to break one mole of bonds in a compound.
The heat released when a substance melts at its melting point.
2. For which of the following substances is the standard enthalpy of formation (ΔH°f) equal to zero?
H₂O(l)
NaCl(s)
O₂(g)
CO₂(g)
3. Hess's Law states that if a reaction can be expressed as the sum of two or more stepwise reactions, the enthalpy change for the overall reaction is the of the enthalpy changes for the individual steps.
4. The standard state for a substance is generally defined as its most stable form at and a pressure of .
5. An exothermic reaction has a positive ΔH value, indicating that heat is absorbed from the surroundings.
True
False
6. The standard enthalpy of formation for a diatomic element like N₂ (g) is always zero.
True
False
7. Calculate the standard enthalpy change (ΔH°rxn) for the following reaction using the given standard heats of formation:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)
Given: ΔH°f [CH₄(g)] = -74.8 kJ/mol, ΔH°f [CO₂(g)] = -393.5 kJ/mol, ΔH°f [H₂O(l)] = -285.8 kJ/mol
8. Observe the energy diagram below. Is the reaction represented by this diagram exothermic or endothermic? Justify your answer.
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