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Chapter 13: Problem 40

A reaction occurs in which 1 mole of \(\mathrm{A}\) is converted to 1 mole of \(B\). If 1 mole of \(A\) has an energy content of \(20 \mathrm{~kJ}\) and 1 mole of \(\mathrm{B}\) has an energy content of \(60 \mathrm{~kJ}\), is this reaction exothermic or endothermic? Calculate \(\Delta E_{\mathrm{rxn}} .\)

Short Answer

Expert verified
The reaction is endothermic with a change in energy of \(\Delta E_{\mathrm{rxn}} = 40 \mathrm{~kJ}\).

Step by step solution

01

Write down the energy content of A and B

The energy content of 1 mole of A is 20 kJ and that of 1 mole of B is 60 kJ.
02

Calculate the change in energy of the reaction, \(\Delta E_{\mathrm{rxn}}\)

The change in energy of the reaction can be calculated using the formula: \[ \Delta E_{\mathrm{rxn}} = E_{\mathrm{final}} - E_{\mathrm{initial}} \] Since 1 mole of A is converted to 1 mole of B, we have \(E_{\mathrm{initial}} = 20 \mathrm{~kJ}\) and \(E_{\mathrm{final}} = 60 \mathrm{~kJ}\). Plugging these values into the formula, we get: \[ \Delta E_{\mathrm{rxn}} = 60 \mathrm{~kJ} - 20 \mathrm{~kJ} = 40 \mathrm{~kJ} \]
03

Determine if the reaction is exothermic or endothermic

Since the value of \(\Delta E_{\mathrm{rxn}}\) is positive, the reaction is endothermic. This means the system absorbed energy from the surroundings as it proceeded. The reaction is endothermic with a change in energy of \(\Delta E_{\mathrm{rxn}} = 40 \mathrm{~kJ}\).

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Most popular questions from this chapter

\(\Delta E_{\mathrm{rxn}}\) for the reaction \(\mathrm{X} \rightarrow \mathrm{Y}\) is \(+30 \mathrm{~kJ}\). (a) Is the reaction endothermic or exothermic? (b) Rewrite the reaction showing heat as either a reactant or a product. (c) What is the value of \(\Delta E_{\mathrm{rxn}}\) for the reverse reaction \(\mathrm{Y} \rightarrow \mathrm{X} ?\) (d) Is the reverse reaction endothermic or exothermic? (e) Will the container in which the forward reaction \(\mathrm{X} \rightarrow\) Y occurs feel hot or cold to the touch? Why?

Consider the reaction \(\mathrm{A}_{2}+\mathrm{B}_{2} \rightarrow 2 \mathrm{AB}\), for which \(\Delta E_{\mathrm{rxn}}=-100 \mathrm{~kJ}\). Forming 1 mole of A \(-B\) bonds releases \(150 \mathrm{~kJ}\). How much energy does it take to break the reactant bonds?

The value of \(\Delta E_{\mathrm{ryn}}\) for an exothermic reaction is always negative. (a) Why is this so in terms of \(E_{\text {reactants }}\) versus \(E_{\text {products }} ?\) (b) Why is this so in terms of bonds broken in the reactants versus bonds formed in the products?

Write the overall balanced chemical equation that goes along with the mechanism: Elementary step 1: \(\mathrm{Cl}_{2} \rightarrow 2 \mathrm{Cl}\) Elementary step \(2: \mathrm{Cl}+\mathrm{CHCl}_{3} \rightarrow \mathrm{HCl}+\mathrm{CCl}_{3}\) Elementary step \(3: \mathrm{Cl}+\mathrm{CCl}_{3} \rightarrow \mathrm{CCl}_{4}\)

Suppose a postulated mechanism does generate the experimental rate law, but the elementary steps, when added together, do not generate the balanced equation for the overall reaction. What can you say about the postulated mechanism?
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