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Chapter 1: Problem 1

Use the following information to answer questions 1-5. \(\begin{array}{ll}{\text { Reaction } 1 : \mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)} & {\Delta H=?} \\ {\text { Reaction } 2 : \mathrm{N}_{2} \mathrm{H}_{4}(l)+\mathrm{CH}_{4} \mathrm{O}(l) \rightarrow \mathrm{CH}_{2} \mathrm{O}(g)+\mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g)} & {\Delta H=-37 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}} \\ {\text { Reaction } 3 : \mathrm{N}_{2}(g)+3 \mathrm{H}_{2}(g) \rightarrow 2 \mathrm{NH}_{3}(g)} & {\Delta H=-46 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}} \\ {\text { Reaction } 4 : \mathrm{CH}_{4} \mathrm{O}(l) \rightarrow \mathrm{CH}_{2} \mathrm{O}(g)+\mathrm{H}_{2}(g)} & {\Delta H=-65 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}}\end{array}\) What is the enthalpy change for reaction 1\(?\) (A) \(-148 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (B) \(-56 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (C) \(-18 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\) (D) \(+148 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\)

Short Answer

Expert verified
The enthalpy change for `Reaction 1` is \(-56 \mathrm{kJ} / \mathrm{mol}_{\mathrm{rxn}}\), thus the correct answer is (B).

Step by step solution

01

Identify reactions that can be used

Notice that Reaction 2 has N2H4 which is the same compound as in Reaction 1. It also forms N2 and H2 gases. The Reaction 3 forms NH3 from N2 and H2 gases. Hence these Reactions can be combined to form Reaction 1.
02

Reverse `Reaction 3` and add `Reaction 2` and `Reaction 3_

By reversing Reaction 3, the enthalpy change also changes its sign from -46 kJ/molrxn to +46 kJ/molrxn. The combined reaction of `Reaction 2` and the reversed `Reaction 3` will be N2H4(l) + CH4O(l) -> CH2O(g) + N2(g) + 3 H2(g) N2(g) + 3 H2(g) -> 2 NH3(g) -> N2H4(l) + CH4O(l) -> CH2O(g) + 2 NH3(g) Note: Since H2 and N2 occur on both sides of the equation, they can be removed when combining the equations.
03

Subtract `Reaction 4` from the combined reaction

Now we have CH4O in both the combined reaction and `Reaction 4`. This allows us to subtract `Reaction 4` from the combined reaction. The enthalpy change of the combined reaction is found by adding the individual enthalpy changes, which gives -37 kJ/molrxn + 46 kJ/molrxn - 65 kJ/molrxn = -56 kJ/molrxn. After subtracting `Reaction 4`, we get N2H4(l) + H2(g) -> 2 NH3(g) which matches the reaction whose ΔH we are looking for, `Reaction 1`.

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Most popular questions from this chapter

\(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(g)\) Based on the information given in the table below, what is \(\Delta H^{\circ}\) for the above reaction? \(\begin{array}{cc}{\text { Bond }} & {\text { Average bond energy }(\mathrm{kJ} / \mathrm{mol})} \\ {\mathrm{H}-\mathrm{H}} & {500} \\\ {\mathrm{O}=\mathrm{O}} & {500} \\ {\mathrm{O}-\mathrm{H}} & {500}\end{array}\) (A) \(-2,000 \mathrm{kJ}\) (B) \(-500 \mathrm{kJ}\) (C) \(+1,000 \mathrm{kJ}\) (D) \(+2,000 \mathrm{kJ}\)

A sealed, rigid container contains three gases: 28.0 \(\mathrm{g}\) of nitrogen, 40.0 \(\mathrm{g}\) of argon, and 36.0 g of water vapor. If the total pressure exerted by the gases is \(2.0 \mathrm{atm},\) what is the partial pressure of the nitrogen? (A) 0.33 atm (B) 0.40 atm (C) 0.50 \(\mathrm{atm}\) (D) 2.0 \(\mathrm{atm}\)

$$\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g) \rightarrow 2 \mathrm{HI}(g)$$ When the reaction given above takes place in a sealed isothermal container, the rate law is $$\text { Rate }=k\left[\mathrm{H}_{2}\right]\left[\mathrm{I}_{2}\right]$$ If a mole of \(\mathrm{H}_{2}\) gas is added to the reaction chamber and the temperature remains constant, which of the following will be true? (A) The rate of reaction and the rate constant will increase. (B) The rate of reaction and the rate constant will not change. (C) The rate of reaction will increase and the rate constant will decrease. (D) The rate of reaction will increase and the rate constant will not change.

The following mechanism is proposed for a reaction: \(\begin{array}{ll}{2 \mathrm{A} \rightarrow \mathrm{B}} & {\text { (fast equilibrium) }} \\ {\mathrm{C}+\mathrm{B} \rightarrow \mathrm{D}} & {\text { (slow) }} \\ {\mathrm{D}+\mathrm{A} \rightarrow \mathrm{E}} & {\text { (fast) }}\end{array}\) Which of the following is the correct rate law for compete reaction? (A) Rate \(=k[\mathrm{C}]^{2}[\mathrm{B}]\) (B) Rate \(=k\left[\mathrm{Cl}[\mathrm{A}]^{2}\right.\) (C) Rate \(=k[\mathrm{C}][\mathrm{A}]^{3}\) (D) Rate \(=k[\mathrm{D}][\mathrm{A}]\)

During a chemical reaction, NO(g) gets reduced and no nitrogen- containing compound is oxidized. Which of the following is a possible product of this reaction? (A) \(\mathrm{NO}_{2}(g)\) (B) \(\mathrm{N}_{2}(g)\) (C) \(\mathrm{NO}_{3}^{-}(a q)\) (D) \(\mathrm{NO}_{2}^{-}(a q)\)
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