Question

calculate the enthalpy for this reaction.
\ce{ch3cl + o2 -> co + hcl + h2o}
use the following thermochemical equations.

1. \ce{2h2 + o2 -> 2h2o} \qquad \delta h_1 = -571\\ \text{kj}
2. \ce{co + 2h2 -> ch3oh} \qquad \delta h_2 = -139\\ \text{kj}
3. \ce{ch3oh + hcl -> ch3cl + h2o} \qquad \delta h_3 = -28\\ \text{kj}

\delta h_{\text{rxn}} = ?\\ \text{kj}
enter either a + or - sign and the magnitude.
use significant figures.

Explanation:

Step1: Reverse Equation 2

Reverse the second equation \( \text{CO} + 2\text{H}_2
ightarrow \text{CH}_3\text{OH} \) to get \( \text{CH}_3\text{OH}
ightarrow \text{CO} + 2\text{H}_2 \). When reversing a reaction, the sign of \( \Delta H \) changes, so \( \Delta H_2' = + 139\ \text{kJ} \).

Step2: Reverse Equation 3

Reverse the third equation \( \text{CH}_3\text{OH} + \text{HCl}
ightarrow \text{CH}_3\text{Cl} + \text{H}_2\text{O} \) to get \( \text{CH}_3\text{Cl} + \text{H}_2\text{O}
ightarrow \text{CH}_3\text{OH} + \text{HCl} \). The sign of \( \Delta H \) changes, so \( \Delta H_3' = + 28\ \text{kJ} \).

Step3: Take Equation 1 as is

The first equation is \( 2\text{H}_2 + \text{O}_2
ightarrow 2\text{H}_2\text{O} \) with \( \Delta H_1 = - 571\ \text{kJ} \).

Step4: Add the modified equations

Now, add the three modified equations:

• Reversed Equation 2: \( \text{CH}_3\text{OH}

ightarrow \text{CO} + 2\text{H}_2 \) (\( \Delta H_2' = + 139\ \text{kJ} \))

• Reversed Equation 3: \( \text{CH}_3\text{Cl} + \text{H}_2\text{O}

ightarrow \text{CH}_3\text{OH} + \text{HCl} \) (\( \Delta H_3' = + 28\ \text{kJ} \))

• Equation 1: \( 2\text{H}_2 + \text{O}_2

ightarrow 2\text{H}_2\text{O} \) (\( \Delta H_1 = - 571\ \text{kJ} \))

Adding these equations:
\( \text{CH}_3\text{OH} + \text{CH}_3\text{Cl} + \text{H}_2\text{O} + 2\text{H}_2 + \text{O}_2
ightarrow \text{CO} + 2\text{H}_2 + \text{CH}_3\text{OH} + \text{HCl} + 2\text{H}_2\text{O} \)

Simplify by canceling out common terms (\( \text{CH}_3\text{OH} \), \( 2\text{H}_2 \), \( \text{H}_2\text{O} \)):
\( \text{CH}_3\text{Cl} + \text{O}_2
ightarrow \text{CO} + \text{HCl} + \text{H}_2\text{O} \) (which is the target reaction)

Now, calculate the total \( \Delta H_{\text{rxn}} \) by adding the \( \Delta H \) values of the modified equations:
\( \Delta H_{\text{rxn}}=\Delta H_1+\Delta H_2'+\Delta H_3' \)
\( \Delta H_{\text{rxn}}=-571 + 139+28 \)
\( \Delta H_{\text{rxn}}=-571+167 \)
\( \Delta H_{\text{rxn}}=-404\ \text{kJ} \)

Answer:

\(-404\)