Hess's Law and change of enthelpy

[Integral0]

The enthalpy of combustion of solid carbon to form carbon dioxide is -393.7 kj/mol carbon, and the enthalpy of combustion of carbon monoxide to form carbon dioxide is -283.3 kj/mol CO. Use these data to calculate change of enthalpy for the reaction

2C(s) + O2(g) -> 2CO(g)

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I'm quite lost . . . after trying this problem for about 20 mins now . . . I still don't see how to use Hess's Law to formulate this answer

What i tried to do was to "form" the equations by the words in the problems.

He are my formulations below; however, I can't seem to get the equation mentioned above.

2CO + O2 -> 2CO2
C + O2 -> CO2

when I rearrange these . . . I can't seem to get 2C(s) + O2(g) -> 2CO(g)

the answer is -220 Kj/mol

thanks

 

[Integral0]

EUREKA! I GOT IT :) :)

2 (C + O2 -> CO2) change in Enthalpy = 2(-394) kj/mol
2CO2 -> O2 + 2CO change in Enthalpy = 2(239.3) kj/mol

= 2C + O2 -> 2CO change in Enthalpy = 221 kj/mol + or - 1 kj/mol

:D ;) :)

 

[ravenprp]

Hess's Law states that the enthalpy change for a reaction is independent of the pathway taken, and only depends on the initial and final states of the reaction. This means that we can use the enthalpy values for different reactions to calculate the enthalpy change for a specific reaction.

In this case, we can use the enthalpy values given for the combustion reactions of solid carbon and carbon monoxide to calculate the enthalpy change for the reaction 2C(s) + O2(g) -> 2CO(g).

First, we can write out the balanced equation for the reaction:

2C(s) + O2(g) -> 2CO(g)

Next, we can use the enthalpy values provided to write out the enthalpy change for each step of the reaction:

Step 1: Combustion of solid carbon to form carbon dioxide
C(s) + O2(g) -> CO2(g)
Enthalpy change = -393.7 kJ/mol

Step 2: Combustion of carbon monoxide to form carbon dioxide
CO(g) + 1/2 O2(g) -> CO2(g)
Enthalpy change = -283.3 kJ/mol

Since we want to calculate the enthalpy change for the reaction 2C(s) + O2(g) -> 2CO(g), we need to multiply the enthalpy change for step 1 by 2, and the enthalpy change for step 2 by 2:

Step 1: 2C(s) + 2O2(g) -> 2CO2(g)
Enthalpy change = -2 * 393.7 kJ/mol = -787.4 kJ/mol

Step 2: 2CO(g) + O2(g) -> 2CO2(g)
Enthalpy change = 2 * (-283.3 kJ/mol) = -566.6 kJ/mol

Now we can add these two enthalpy changes together to get the overall enthalpy change for the reaction:

Enthalpy change = -787.4 kJ/mol + (-566.6 kJ/mol) = -1354 kJ/mol

However, we need to remember that the enthalpy change for step 2 is for the formation of 2 moles of CO(g), while the reaction only produces 1 mole of CO(g). Therefore,