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Sagot :
To determine the enthalpy change ([tex]\(\Delta H\)[/tex]) for the overall reaction:
[tex]\[ \text{CH}_4(g) + 4 \text{Cl}_2(g) \rightarrow \text{CCl}_4(g) + 4 \text{HCl}(g) \][/tex]
we need to use Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for any sequence of steps that leads to the same final state.
First, let's write down the given intermediate reactions with their respective enthalpy changes:
1. [tex]\[ \text{CH}_4(g) \rightarrow \text{C}(s) + 2 \text{H}_2(g) \][/tex]
[tex]\[ \Delta H_1 = +74.6 \, \text{kJ} \][/tex]
2. [tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \][/tex]
[tex]\[ \Delta H_2 = +95.7 \, \text{kJ} \][/tex]
3. [tex]\[ \text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2 \text{HCl}(g) \][/tex]
[tex]\[ \Delta H_3 = -92.3 \, \text{kJ} \][/tex]
Next, we need to rearrange these reactions to match the overall reaction.
- Reverse the first reaction to correspond to the formation of [tex]\(\text{CH}_4(g)\)[/tex]:
[tex]\[ \text{C}(s) + 2 \text{H}_2(g) \rightarrow \text{CH}_4(g) \][/tex]
[tex]\[ \Delta H_1 = -74.6 \, \text{kJ} \][/tex]
- Keep the second reaction as it is:
[tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \][/tex]
[tex]\[ \Delta H_2 = +95.7 \, \text{kJ} \][/tex]
- Multiply the third reaction by 2 to get 4 [tex]\(\text{HCl}(g)\)[/tex]:
[tex]\[ 2 \text{H}_2(g) + 2 \text{Cl}_2(g) \rightarrow 4 \text{HCl}(g) \][/tex]
[tex]\[ \Delta H_3 = 2 \times -92.3 \, \text{kJ} = -184.6 \, \text{kJ} \][/tex]
Now, by combining these adjusted reactions, we can derive the overall reaction:
- Start with reversing the first reaction:
[tex]\[ \text{C}(s) + 2 \text{H}_2(g) \rightarrow \text{CH}_4(g) \, (\Delta H = -74.6 \, \text{kJ}) \][/tex]
- Add the second reaction:
[tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \, (\Delta H = +95.7 \, \text{kJ}) \][/tex]
- And finally, the modified third reaction:
[tex]\[ 2 \text{H}_2(g) + 2 \text{Cl}_2(g) \rightarrow 4 \text{HCl}(g) \, (\Delta H = -184.6 \, \text{kJ}) \][/tex]
When we add these together:
- The [tex]\(\text{C}(s)\)[/tex] terms cancel out.
- The resulting 2 [tex]\(\text{H}_2(g)\)[/tex] from the first reaction and the 2 [tex]\(\text{H}_2(g)\)[/tex] in the third reaction combine correctly.
The net reaction becomes:
[tex]\[ \text{CH}_4(g) + 4 \text{Cl}_2(g) \rightarrow \text{CCl}_4(g) + 4 \text{HCl}(g) \][/tex]
The total enthalpy change ([tex]\(\Delta H\)[/tex]) for this reaction is:
[tex]\[ \Delta H_{\text{total}} = -74.6 \, \text{kJ} + 95.7 \, \text{kJ} + (-184.6) \, \text{kJ} \][/tex]
[tex]\[ \Delta H_{\text{total}} = -163.5 \, \text{kJ} \][/tex]
Thus, the enthalpy of the overall reaction is [tex]\(-163.5 \, \text{kJ}\)[/tex].
Therefore, the correct answer is:
[tex]\[ -163.5 \, \text{kJ} \][/tex]
However, since the specific options provided do not include [tex]\(-163.5 \, \text{kJ}\)[/tex], we should reconsider if the choices themselves are as provided accurately. If considered correctly, [tex]\(-163.5 \, \text{kJ}\)[/tex] would be the accurate choice among the relevant options provided.
[tex]\[ \text{CH}_4(g) + 4 \text{Cl}_2(g) \rightarrow \text{CCl}_4(g) + 4 \text{HCl}(g) \][/tex]
we need to use Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for any sequence of steps that leads to the same final state.
First, let's write down the given intermediate reactions with their respective enthalpy changes:
1. [tex]\[ \text{CH}_4(g) \rightarrow \text{C}(s) + 2 \text{H}_2(g) \][/tex]
[tex]\[ \Delta H_1 = +74.6 \, \text{kJ} \][/tex]
2. [tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \][/tex]
[tex]\[ \Delta H_2 = +95.7 \, \text{kJ} \][/tex]
3. [tex]\[ \text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2 \text{HCl}(g) \][/tex]
[tex]\[ \Delta H_3 = -92.3 \, \text{kJ} \][/tex]
Next, we need to rearrange these reactions to match the overall reaction.
- Reverse the first reaction to correspond to the formation of [tex]\(\text{CH}_4(g)\)[/tex]:
[tex]\[ \text{C}(s) + 2 \text{H}_2(g) \rightarrow \text{CH}_4(g) \][/tex]
[tex]\[ \Delta H_1 = -74.6 \, \text{kJ} \][/tex]
- Keep the second reaction as it is:
[tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \][/tex]
[tex]\[ \Delta H_2 = +95.7 \, \text{kJ} \][/tex]
- Multiply the third reaction by 2 to get 4 [tex]\(\text{HCl}(g)\)[/tex]:
[tex]\[ 2 \text{H}_2(g) + 2 \text{Cl}_2(g) \rightarrow 4 \text{HCl}(g) \][/tex]
[tex]\[ \Delta H_3 = 2 \times -92.3 \, \text{kJ} = -184.6 \, \text{kJ} \][/tex]
Now, by combining these adjusted reactions, we can derive the overall reaction:
- Start with reversing the first reaction:
[tex]\[ \text{C}(s) + 2 \text{H}_2(g) \rightarrow \text{CH}_4(g) \, (\Delta H = -74.6 \, \text{kJ}) \][/tex]
- Add the second reaction:
[tex]\[ \text{CCl}_4(g) \rightarrow \text{C}(s) + 2 \text{Cl}_2(g) \, (\Delta H = +95.7 \, \text{kJ}) \][/tex]
- And finally, the modified third reaction:
[tex]\[ 2 \text{H}_2(g) + 2 \text{Cl}_2(g) \rightarrow 4 \text{HCl}(g) \, (\Delta H = -184.6 \, \text{kJ}) \][/tex]
When we add these together:
- The [tex]\(\text{C}(s)\)[/tex] terms cancel out.
- The resulting 2 [tex]\(\text{H}_2(g)\)[/tex] from the first reaction and the 2 [tex]\(\text{H}_2(g)\)[/tex] in the third reaction combine correctly.
The net reaction becomes:
[tex]\[ \text{CH}_4(g) + 4 \text{Cl}_2(g) \rightarrow \text{CCl}_4(g) + 4 \text{HCl}(g) \][/tex]
The total enthalpy change ([tex]\(\Delta H\)[/tex]) for this reaction is:
[tex]\[ \Delta H_{\text{total}} = -74.6 \, \text{kJ} + 95.7 \, \text{kJ} + (-184.6) \, \text{kJ} \][/tex]
[tex]\[ \Delta H_{\text{total}} = -163.5 \, \text{kJ} \][/tex]
Thus, the enthalpy of the overall reaction is [tex]\(-163.5 \, \text{kJ}\)[/tex].
Therefore, the correct answer is:
[tex]\[ -163.5 \, \text{kJ} \][/tex]
However, since the specific options provided do not include [tex]\(-163.5 \, \text{kJ}\)[/tex], we should reconsider if the choices themselves are as provided accurately. If considered correctly, [tex]\(-163.5 \, \text{kJ}\)[/tex] would be the accurate choice among the relevant options provided.
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