Use Hess's Law to find the change in heat of 2C(graphite)+H2(g)-->C2H2(g)?
Given:
C(graphite) + O2(g) --> CO2(g) change of heat rxn = -393.5 kJ
2H2 (g) + O2(g) ---> 2H2O (l) change of heat rxn = -571.6 kJ
2C2H2 (g) +5O2(g) ----> 4CO2(g) +2H2O (l) change of heat rxn = -2598.8 kJ
And please show how you found the amount in each of the equations...I'm confused whether or not I should multiply 2 on the first equation or use the amount as it is and if I should divide by 2 for the second equation because there is twice as much H2 in the second equation because there is twice as much as in the first given equation.
To find the change in heat of the given reaction using Hess's Law, we need to manipulate and combine the given equations in a way that cancels out the reactants and products not involved in the desired reaction.
Let's start by writing down the balanced equation for the desired reaction:
2C(graphite) + H2(g) --> C2H2(g)
Now, let's look at the given equations and their corresponding change in heat values:
1. C(graphite) + O2(g) --> CO2(g) ∆H1 = -393.5 kJ
2. 2H2(g) + O2(g) --> 2H2O(l) ∆H2 = -571.6 kJ
3. 2C2H2(g) + 5O2(g) --> 4CO2(g) + 2H2O(l) ∆H3 = -2598.8 kJ
Here's how we can use these equations to find the change in heat for the desired reaction:
Step 1: Multiply equation 1 by 2 to get the same number of carbon atoms as in the desired reaction:
2C(graphite) + 2O2(g) -> 2CO2(g) (∆H1' = -787.0 kJ)
Step 2: Multiply equation 2 by 2 and reverse it to get the same number of hydrogen gas molecules:
4H2O(l) -> 4H2(g) + 2O2(g) (∆H2' = +1432.8 kJ)
Step 3: Manipulate equation 3 to match the stoichiometry of the desired reaction:
2C2H2(g) + 5O2(g) -> 4CO2(g) + 2H2O(l) (∆H3' = -2598.8 kJ)
Step 4: Add equations 1', 2', and 3' to obtain the desired reaction:
2C(graphite) + H2(g) -> C2H2(g) (∆H = ?)
2C(graphite) + 2O2(g) -> 2CO2(g) (∆H1' = -787.0 kJ)
4H2O(l) -> 4H2(g) + 2O2(g) (∆H2' = +1432.8 kJ)
2C2H2(g) + 5O2(g) -> 4CO2(g) + 2H2O(l) (∆H3' = -2598.8 kJ)
Step 5: Sum up the changes in heat values to find the overall change in heat for the desired reaction:
∆H = ∆H1' + ∆H2' + ∆H3'
= -787.0 kJ + 1432.8 kJ - 2598.8 kJ
Therefore, the change in heat (∆H) for the reaction 2C(graphite) + H2(g) -> C2H2(g) is (-787.0 kJ + 1432.8 kJ - 2598.8 kJ) = -1953.0 kJ.