Calculate DeltaHrxn for the following reaction:
C + H2O --> CO + H2
Use the following:
C + O2 --> CO2 DeltaH = -393.5 kJ
2CO + O2 --> 2CO2 DeltaH = -566.0 kJ
2H2 + O2 --> 2H2O Delta H = -483.6 kJ
DeltaHrxn = ?
equation 1 as is.
#2 reverse and take 1/2
#3 reverse and take 1/2
To calculate DeltaHrxn for the given reaction, we need to use Hess's law, which states that the enthalpy change of a reaction is independent of the pathway taken and depends only on the initial and final states.
The given reaction can be written as a combination of the following reactions:
1) C + O2 --> CO2
2) H2 + 1/2O2 --> H2O
3) CO2 + H2 --> CO + H2O
Since we want to calculate DeltaHrxn for the reaction C + H2O --> CO + H2, we need to manipulate the above reactions in order to cancel out any common reactants and products.
First, we need to reverse the first reaction (equation 1) and multiply it by 2 to cancel out the CO2 in the third reaction (equation 3):
-2(C + O2 --> CO2) DeltaH = -2(-393.5 kJ) = 787.0 kJ
Next, multiply the second reaction (equation 2) by 2 to cancel out the H2O in the third reaction (equation 3):
-2(H2 + 1/2O2 --> H2O) DeltaH = -2(-483.6 kJ) = 967.2 kJ
Now, add the modified equations 1 and 2 to obtain the desired reaction:
-2(C + O2 --> CO2) + -2(H2 + 1/2O2 --> H2O) DeltaHrxn = 787.0 kJ + 967.2 kJ = 1754.2 kJ
Therefore, DeltaHrxn for the reaction C + H2O --> CO + H2 is 1754.2 kJ.