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Multiple Choice
Which equation represents the standard enthalpy of formation, ΔH⦵f, for CHCl3(l)?
A
CHCl3(l) → C(s) + H(g) + 3 Cl(g)
B
C(s) + 1/2 H2(g) + 3/2 Cl2(g) → CHCl3(l)
C
2 C(s) + H2(g) + 3 Cl2(g) → 2 CHCl3(l)
D
C(s) + H(g) + 3 Cl(g) → CHCl3(l)
Verified step by step guidance
1
Understand the concept of standard enthalpy of formation, ΔH⦵f. It is defined as the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions (1 atm pressure and 298 K).
Identify the elements in their standard states. For carbon, the standard state is solid graphite (C(s)). For hydrogen, it is diatomic hydrogen gas (H2(g)). For chlorine, it is diatomic chlorine gas (Cl2(g)).
Write the balanced chemical equation for the formation of one mole of CHCl3(l) from its elements in their standard states. This involves combining carbon, hydrogen, and chlorine in their standard states to form CHCl3(l).
Ensure the equation is balanced with respect to the number of atoms of each element. Since CHCl3(l) contains one carbon atom, one hydrogen atom, and three chlorine atoms, the equation should reflect these proportions.
The correct equation representing the standard enthalpy of formation for CHCl3(l) is: C(s) + 1/2 H2(g) + 3/2 Cl2(g) → CHCl3(l). This equation shows the formation of one mole of CHCl3(l) from its elements in their standard states.