Given the following chemical reactions and their respective enthalpy changes
C2H2 + 5/2 O2-------- 2CO2 +H2O -1299.6 KJmol
C + 1/2 O2----------CO2 -393KJmol
H2 + 1/2 O2--------H2O -285.9KJmol
Calculate the Delta H for the reaction
2C + H2--------C2H2
Note your equation 2 is not balanced. It should be C + O2 ==> CO2. I don't know if dH is correct or not. Check it. This is eqn 2.
What you want to do is this.
Add 2 times eqn 2 to eqn 3 and to the reverse of eqn 1. If you multiply an equation you must multiply the dH value too. If you reverse an equation you must use the negative of dH for that eqn.
Check to make SURE that these manipulations will give you the new eqn you want.
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To calculate the delta H for the given reaction, we can use the Hess's Law. Hess's Law states that the overall enthalpy change of a reaction is the sum of the enthalpy changes of the individual reactions, as long as the reactants and products are the same.
Here's how you can calculate the delta H for the reaction "2C + H2 -> C2H2" using Hess's Law:
1. Start with the given reactants and product: 2C + H2 -> C2H2.
2. Look for the individual reactions in the given list that have the same reactants and products, but with the coefficients that match the coefficients in the target reaction. In this case, we can use the following reactions:
a) C2H2 + 5/2 O2 -> 2CO2 + H2O (-1299.6 KJ/mol)
b) 2C + 1/2 O2 -> 2CO2 (-2 * -393 KJ/mol)
c) H2 + 1/2 O2 -> H2O (-285.9 KJ/mol)
3. Multiply the enthalpy change of each individual reaction by a factor (if needed) so that the coefficients of the reactants and products match the target reaction.
For reaction (a):
Multiply the enthalpy change by 2 to match the coefficient of C2H2 in the target reaction:
2 * (-1299.6 KJ/mol) = -2599.2 KJ/mol
For reaction (b):
Multiply the enthalpy change by 1 to match the coefficient of 2C in the target reaction:
1 * (-2 * -393 KJ/mol) = +786 KJ/mol
For reaction (c):
Multiply the enthalpy change by 1 to match the coefficient of H2 in the target reaction:
1 * (-285.9 KJ/mol) = -285.9 KJ/mol
4. Add up the enthalpy changes of the individual reactions to find the enthalpy change of the target reaction:
-2599.2 KJ/mol + 786 KJ/mol - 285.9 KJ/mol = -2099.1 KJ/mol
Therefore, the delta H for the reaction "2C + H2 -> C2H2" is -2099.1 KJ/mol.