Question

From the information given below, write an equation for the enthalpy change in reaction 3:

(1) F(g) -> D(s) + E(g) (∆ H₁)
(2) F(s) -> F(g) (∆H₂)
(3) D(s) + E(g) -> F(s) (∆H₃ )
O Equation A
O Equation B
O Equation C
O Equation D
(A) ∆H₃ = - ∆H₁ + - ∆H₂
(B) ∆H₃ = - ∆H₁ + ∆H₂
(C) ∆H₃ = ∆H₁ + ∆H₂
(D) ∆H₃ = ∆H₁ + - ∆H₂

Answer 1

The enthalpy change for reaction 3, using Hess's Law, is derived from reversing reaction 1 and adding reaction 2 to it. The correct equation for the enthalpy change in reaction 3 is ΔH₃ = - ΔH₁ + ΔH₂, which corresponds to Equation B.

Step-by-step explanation:

To solve for the enthalpy change in reaction 3, we need to apply Hess's Law, which states that the total enthalpy change for a reaction is the sum of all individual steps that lead to the final reaction. The given reactions (1) and (2) can be manipulated to derive the enthalpy change for reaction (3). We start by reversing reaction (1) and then adding reaction (2) to it, as follows:

• Reverse of (1): D(s) + E(g) → F(g) (ΔH = - ΔH₁)
• (2) As is: F(s) → F(g) (ΔH = ΔH₂)

Adding these two equations gives us reaction (3): D(s) + E(g) → F(s), and the enthalpy change for this reaction (ΔH₃) is the sum of the enthalpy changes of the two manipulated reactions:

ΔH₃ = - ΔH₁ + ΔH₂

Therefore, the correct answer is Equation B, ΔH₃ = - ΔH₁ + ΔH₂.