Can someone PLEASE help me with this???? I am soooo confused with this problem!!!
Combustion reactions involve reacting When compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. Using the enthalpies of combustion for C4H4 (-2341 kJ/mol), C4H8 (-2766 kJ/mol) and H2 (-286 kJ/mol), calculate delta H for the reaction
C4H4(g) + 2H2(g) --> C4H8(g)
(1)C4H4 + 5 O2 ==> 4CO2 + 2H2O -2341 kJ/mol
(2)C4H8 + 6 O2 ==> 4CO2 + 4H2O -2766 kJ/mol
(3)H2 + 1/2 O2 ==> H2O -286 kJ/mol
Add equation 1, to reversed equation 2, to twice equation 3 and you should get the equation you want of C4H4 + 2H2 ==> C4H8.
Remember to change the sign of equations that are reversed and to multiply the kJ/mol of equations that are multiplied. Post your work if you get stuck.
Thanks SO much for the help!:)
Sure, I can help you with that!
To calculate the delta H for the reaction, you need to use Hess's Law and the enthalpies of combustion for each compound involved.
Hess's Law states that the enthalpy change for a chemical reaction is independent of the pathway taken. This means that you can add or subtract reactions to get the desired reaction and then sum up the corresponding enthalpy changes.
Here's how to solve it step by step:
1. Start by writing out the given reaction and the enthalpies of combustion for each compound involved:
C4H4(g) + 2H2(g) --> C4H8(g)
ΔH°combustion for C4H4 = -2341 kJ/mol
ΔH°combustion for C4H8 = -2766 kJ/mol
ΔH°combustion for H2 = -286 kJ/mol
2. Multiply the combustion reactions for C4H4 and H2 by the coefficients in the target reaction so that you end up with an overall reaction that matches the target reaction:
C4H4(g) + 6H2(g) --> 2C4H8(g) (multiplied the C4H4 combustion by 3, and H2 combustion by 3)
3. Now, we can sum up the enthalpies of combustion to calculate the delta H for the overall reaction:
ΔH°overall = ∑ΔH°products - ∑ΔH°reactants
ΔH°overall = [2(-2766 kJ/mol)] - [(-2341 kJ/mol) + 6(-286 kJ/mol)]
ΔH°overall = -5532 kJ/mol + 1706 kJ/mol
ΔH°overall = -3826 kJ/mol
Therefore, the delta H for the reaction C4H4(g) + 2H2(g) --> C4H8(g) is -3826 kJ/mol.
I hope this explanation helps you understand how to calculate delta H for combustion reactions using enthalpies of combustion and Hess's Law!