Multiple Choice
What is the standard enthalpy change (∆Hrxn) for the reaction 2 CHCl3(l) → 2 C(s) + H2(g) + 3 Cl2(g) given the standard enthalpy of formation of CHCl3(l) is -134.1 kJ/mol?
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8. Thermochemistry
Enthalpy of Formation
Multiple Choice
Which equation represents the standard enthalpy of formation, ΔH°f, for CHCl3(l)?
A
2 C(s) + H2(g) + 3 Cl2(g) → 2 CHCl3(l)
B
C(s) + H(g) + 3 Cl(g) → CHCl3(l)
C
C(s) + 1/2 H2(g) + 3/2 Cl2(g) → CHCl3(l)
D
CHCl3(l) → C(s) + H(g) + 3 Cl(g)
Verified step by step guidance1
Understand the concept of standard enthalpy of formation (ΔH°f): It is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.
Identify the elements in their standard states: Carbon (C) as graphite, Hydrogen (H2) as a diatomic gas, and Chlorine (Cl2) as a diatomic gas.
Write the balanced chemical equation for the formation of one mole of CHCl3(l) from its elements in their standard states: C(s) + 1/2 H2(g) + 3/2 Cl2(g) → CHCl3(l).
Ensure that the equation is balanced with respect to both mass and moles, particularly focusing on forming exactly one mole of the compound.
Verify that the equation represents the formation of the compound from its elements in their most stable forms under standard conditions (1 atm pressure and 25°C).
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