Reactivity 1.2.2—Hess’s law states that the enthalpy change for a reaction is independent of the pathway between the initial and final states. Apply Hess’s law to calculate enthalpy changes in multistep reactions.

What is the enthalpy change of reaction for the following equation?

C₂H₄ (g) + H₂ (g) → C₂H₆ (g)

C₂H₄ (g) + 3O₂ (g) → 2CO₂ (g) + 2H₂O (l)        ΔH = x

C₂H₆ (g) + $\frac{7}{2}$O₂ (g) → 2CO₂ (g) + 3H₂O (l)    ΔH = y

H₂ (g) + $\frac{1}{2}$O₂ (g) → H₂O (l)                           ΔH = z

A. x + y + z

B. −x − y + z

C. x − y − z

D. x − y + z

What is the enthalpy change of reaction for the following equation?

C₂H₄ (g) + H₂ (g) → C₂H₆ (g)

C₂H₄ (g) + 3O₂ (g) → 2CO₂ (g) + 2H₂O (l)        ΔH = x

C₂H₆ (g) + $\frac{7}{2}$O₂ (g) → 2CO₂ (g) + 3H₂O (l)    ΔH = y

H₂ (g) + $\frac{1}{2}$O₂ (g) → H₂O (l)                           ΔH = z

A. x + y + z

B. −x − y + z

C. x − y − z

D. x − y + z

What is the enthalpy change of reaction for the following equation?

C₂H₄ (g) + H₂ (g) → C₂H₆ (g)

C₂H₄ (g) + 3O₂ (g) → 2CO₂ (g) + 2H₂O (l)        ΔH = x

C₂H₆ (g) + $\frac{7}{2}$O₂ (g) → 2CO₂ (g) + 3H₂O (l)    ΔH = y

H₂ (g) + $\frac{1}{2}$O₂ (g) → H₂O (l)                           ΔH = z

A. x + y + z

B. −x − y + z

C. x − y − z

D. x − y + z

What is the enthalpy change of reaction for the following equation?

C₂H₄ (g) + H₂ (g) → C₂H₆ (g)

C₂H₄ (g) + 3O₂ (g) → 2CO₂ (g) + 2H₂O (l)        ΔH = x

C₂H₆ (g) + $\frac{7}{2}$O₂ (g) → 2CO₂ (g) + 3H₂O (l)    ΔH = y

H₂ (g) + $\frac{1}{2}$O₂ (g) → H₂O (l)                           ΔH = z

A. x + y + z

B. −x − y + z

C. x − y − z

D. x − y + z

Consider the following equations.

2Al (s) + $\frac{3}{2}$O₂ (g) → Al₂O₃ (s)    ΔH^Ɵ = −1670 kJ
Mn (s) + O₂ (g) → MnO₂ (s)    ΔH^Ɵ = −520 kJ

What is the standard enthalpy change, in kJ, of the reaction below?

4Al (s) + 3MnO₂ (s) → 2Al₂O₃ (s) + 3Mn (s)

A. −1670 + 520

B. $\frac{3}{2}$(−1670) + 3(520)

C. 2(−1670) + 3(−520)

D. 2(−1670) + 3(520)

Consider the following equations.

2Al (s) + $\frac{3}{2}$O₂ (g) → Al₂O₃ (s)    ΔH^Ɵ = −1670 kJ
Mn (s) + O₂ (g) → MnO₂ (s)    ΔH^Ɵ = −520 kJ

What is the standard enthalpy change, in kJ, of the reaction below?

4Al (s) + 3MnO₂ (s) → 2Al₂O₃ (s) + 3Mn (s)

A. −1670 + 520

B. $\frac{3}{2}$(−1670) + 3(520)

C. 2(−1670) + 3(−520)

D. 2(−1670) + 3(520)

Consider the following equations.

2Al (s) + $\frac{3}{2}$O₂ (g) → Al₂O₃ (s)    ΔH^Ɵ = −1670 kJ
Mn (s) + O₂ (g) → MnO₂ (s)    ΔH^Ɵ = −520 kJ

What is the standard enthalpy change, in kJ, of the reaction below?

4Al (s) + 3MnO₂ (s) → 2Al₂O₃ (s) + 3Mn (s)

A. −1670 + 520

B. $\frac{3}{2}$(−1670) + 3(520)

C. 2(−1670) + 3(−520)

D. 2(−1670) + 3(520)

Consider the following equations.

2Al (s) + $\frac{3}{2}$O₂ (g) → Al₂O₃ (s)    ΔH^Ɵ = −1670 kJ
Mn (s) + O₂ (g) → MnO₂ (s)    ΔH^Ɵ = −520 kJ

What is the standard enthalpy change, in kJ, of the reaction below?

4Al (s) + 3MnO₂ (s) → 2Al₂O₃ (s) + 3Mn (s)

A. −1670 + 520

B. $\frac{3}{2}$(−1670) + 3(520)

C. 2(−1670) + 3(−520)

D. 2(−1670) + 3(520)

What is the enthalpy change of the reaction?

C₆H₁₄ (l) → C₂H₄ (g) + C₄H₁₀ (g)

A.  + 1411 + 2878 + 4163

B.  + 1411 − 2878 − 4163

C.  + 1411 + 2878 − 4163

D.  − 1411 − 2878 + 4163

What is the enthalpy change of the reaction?

C₆H₁₄ (l) → C₂H₄ (g) + C₄H₁₀ (g)

A.  + 1411 + 2878 + 4163

B.  + 1411 − 2878 − 4163

C.  + 1411 + 2878 − 4163

D.  − 1411 − 2878 + 4163

What is the enthalpy change of the reaction?

C₆H₁₄ (l) → C₂H₄ (g) + C₄H₁₀ (g)

A.  + 1411 + 2878 + 4163

B.  + 1411 − 2878 − 4163

C.  + 1411 + 2878 − 4163

D.  − 1411 − 2878 + 4163

What is the enthalpy change of the reaction?

C₆H₁₄ (l) → C₂H₄ (g) + C₄H₁₀ (g)

A.  + 1411 + 2878 + 4163

B.  + 1411 − 2878 − 4163

C.  + 1411 + 2878 − 4163

D.  − 1411 − 2878 + 4163

Which combination will give you the enthalpy change for the hydrogenation of ethene to ethane, $∆H_3$?

A.  $-∆H_2+∆H_1-∆H_4$

B.  $∆H_2\mathit{-}∆H_1+∆H_4$

C.  $∆H_2+∆H_1-∆H_4$

D.  $-∆H_2\mathit{-}∆H_1+∆H_4$

Which combination will give you the enthalpy change for the hydrogenation of ethene to ethane, $∆H_3$?

A.  $-∆H_2+∆H_1-∆H_4$

B.  $∆H_2\mathit{-}∆H_1+∆H_4$

C.  $∆H_2+∆H_1-∆H_4$

D.  $-∆H_2\mathit{-}∆H_1+∆H_4$

Which combination will give you the enthalpy change for the hydrogenation of ethene to ethane, $∆H_3$?

A.  $-∆H_2+∆H_1-∆H_4$

B.  $∆H_2\mathit{-}∆H_1+∆H_4$

C.  $∆H_2+∆H_1-∆H_4$

D.  $-∆H_2\mathit{-}∆H_1+∆H_4$

Which combination will give you the enthalpy change for the hydrogenation of ethene to ethane, $∆H_3$?

A.  $-∆H_2+∆H_1-∆H_4$

B.  $∆H_2\mathit{-}∆H_1+∆H_4$

C.  $∆H_2+∆H_1-∆H_4$

D.  $-∆H_2\mathit{-}∆H_1+∆H_4$

What is the enthalpy change of the reaction, in kJ?

2C (graphite) + O₂(g) → 2CO (g)

A.  −394 − 283

B.  2(−394) + 2(−283)

C.  −394 + 283

D.  2(−394) + 2(283)

What is the enthalpy change of the reaction, in kJ?

2C (graphite) + O₂(g) → 2CO (g)

A.  −394 − 283

B.  2(−394) + 2(−283)

C.  −394 + 283

D.  2(−394) + 2(283)

What is the enthalpy change of the reaction, in kJ?

2C (graphite) + O₂(g) → 2CO (g)

A.  −394 − 283

B.  2(−394) + 2(−283)

C.  −394 + 283

D.  2(−394) + 2(283)

What is the enthalpy change of the reaction, in kJ?

2C (graphite) + O₂(g) → 2CO (g)

A.  −394 − 283

B.  2(−394) + 2(−283)

C.  −394 + 283

D.  2(−394) + 2(283)

Which combination of ΔH₁, ΔH₂, and ΔH₃ would give the enthalpy of the reaction?

CS₂(l) + 3O₂(g) → CO₂(g) + 2SO₂(g)

ΔH₁  C (s) + O₂(g) → CO₂(g)
ΔH₂  S (s) + O₂(g) → SO₂(g)
ΔH₃  C (s) + 2S (s) → CS₂(l)

A.  ΔH = ΔH₁ + ΔH₂ + ΔH₃

B.  ΔH = ΔH₁ + ΔH₂ − ΔH₃

C.  ΔH = ΔH₁ + 2(ΔH₂) + ΔH₃

D.  ΔH = ΔH₁ + 2(ΔH₂) − ΔH₃

Which combination of ΔH₁, ΔH₂, and ΔH₃ would give the enthalpy of the reaction?

CS₂(l) + 3O₂(g) → CO₂(g) + 2SO₂(g)

ΔH₁  C (s) + O₂(g) → CO₂(g)
ΔH₂  S (s) + O₂(g) → SO₂(g)
ΔH₃  C (s) + 2S (s) → CS₂(l)

A.  ΔH = ΔH₁ + ΔH₂ + ΔH₃

B.  ΔH = ΔH₁ + ΔH₂ − ΔH₃

C.  ΔH = ΔH₁ + 2(ΔH₂) + ΔH₃

D.  ΔH = ΔH₁ + 2(ΔH₂) − ΔH₃

Which combination of ΔH₁, ΔH₂, and ΔH₃ would give the enthalpy of the reaction?

CS₂(l) + 3O₂(g) → CO₂(g) + 2SO₂(g)

ΔH₁  C (s) + O₂(g) → CO₂(g)
ΔH₂  S (s) + O₂(g) → SO₂(g)
ΔH₃  C (s) + 2S (s) → CS₂(l)

A.  ΔH = ΔH₁ + ΔH₂ + ΔH₃

B.  ΔH = ΔH₁ + ΔH₂ − ΔH₃

C.  ΔH = ΔH₁ + 2(ΔH₂) + ΔH₃

D.  ΔH = ΔH₁ + 2(ΔH₂) − ΔH₃

Which combination of ΔH₁, ΔH₂, and ΔH₃ would give the enthalpy of the reaction?

CS₂(l) + 3O₂(g) → CO₂(g) + 2SO₂(g)

ΔH₁  C (s) + O₂(g) → CO₂(g)
ΔH₂  S (s) + O₂(g) → SO₂(g)
ΔH₃  C (s) + 2S (s) → CS₂(l)

A.  ΔH = ΔH₁ + ΔH₂ + ΔH₃

B.  ΔH = ΔH₁ + ΔH₂ − ΔH₃

C.  ΔH = ΔH₁ + 2(ΔH₂) + ΔH₃

D.  ΔH = ΔH₁ + 2(ΔH₂) − ΔH₃