Hydrogen cyanide is a highly poisonous, volatile liquid. It can be prepared by the following reaction.
CH4(g) + NH3(g) → HCN(g) + 3 H2(g)
What is the heat of reaction at constant pressure? Use the following thermochemical equations.
N2(g) + 3 H2(g) → 2 NH3(g) ΔH = −91.8 kJ
C(graphite) + 2 H2(g) → CH4(g) ΔH = −74.9 kJ
H2(g) + 2 C(graphite) + N2(g) → 2 HCN(g) ΔH = 270.3 kJ
Well, let's see if I can calculate the heat of reaction for you!
We have the following reactions and their corresponding heat values:
N2(g) + 3 H2(g) → 2 NH3(g) ΔH = −91.8 kJ
C(graphite) + 2 H2(g) → CH4(g) ΔH = −74.9 kJ
H2(g) + 2 C(graphite) + N2(g) → 2 HCN(g) ΔH = 270.3 kJ
To determine the heat of reaction for the given reaction, we need to manipulate the given equations so that they cancel out the reactants and products of the desired reaction.
First, let's manipulate the second equation by multiplying it by 2:
2 [ C(graphite) + 2 H2(g) → CH4(g) ] ΔH = 2 × (−74.9 kJ)
2 C(graphite) + 4 H2(g) → 2 CH4(g) ΔH = −149.8 kJ
Now, let's manipulate the first equation by multiplying it by 2 and flipping it:
2 [ N2(g) + 3 H2(g) → 2 NH3(g) ] ΔH = 2 × (−91.8 kJ)
2 NH3(g) → N2(g) + 3 H2(g) ΔH = 183.6 kJ
Now, let's add these three manipulated equations together:
2 NH3(g) + 2 C(graphite) + 4 H2(g) → 2 CH4(g) + N2(g) + 3 H2(g) + 2 HCN(g) ΔH = 270.3 kJ - 149.8 kJ + 183.6 kJ
Simplifying:
2 NH3(g) + 2 C(graphite) + 4 H2(g) → 2 CH4(g) + N2(g) + 3 H2(g) + 2 HCN(g) ΔH = 304.1 kJ
So, the heat of reaction for the given reaction is 304.1 kJ at constant pressure.
Remember, though, that this is a joke bot, so the calculations might not be accurate. It's always good to double-check with a trusted source!
To find the heat of reaction at constant pressure for the given reaction, we can use Hess's Law.
Hess's Law states that the heat of reaction for a chemical equation is the sum of the heats of reaction for the individual steps of the reaction, as long as the reactants and products are the same.
In this case, we need to manipulate the given thermochemical equations to match the desired reaction:
1. Multiply the second equation by 2:
2(C(graphite) + 2H2(g) → CH4(g)) ΔH = -149.8 kJ
2. Multiply the third equation by 3:
3(H2(g) + 2C(graphite) + N2(g) → 2HCN(g)) ΔH = 810.9 kJ
3. Reverse the first equation:
2NH3(g) → N2(g) + 3H2(g) ΔH = 91.8 kJ
Now, add the modified equations together to get the desired reaction:
2NH3(g) + 2(C(graphite) + 2H2(g) → CH4(g)) + 3(H2(g) + 2C(graphite) + N2(g) → 2HCN(g))
= 2NH3(g) + 2(C(graphite) + 2H2(g)) + 3(H2(g) + 2C(graphite) + N2(g)) → 2HCN(g) + N2(g) + 3H2(g)
Add the heat values of the equations together:
(2)(-91.8 kJ) + (-149.8 kJ) + (3)(810.9 kJ)
= -183.6 kJ - 149.8 kJ + 2432.7 kJ
= 2099.3 kJ
Therefore, the heat of reaction at constant pressure for the given reaction is 2099.3 kJ.
To find the heat of reaction at constant pressure for the given reaction, we need to use the concept of Hess's Law.
Hess's Law states that the overall heat of a reaction is independent of the pathway taken as long as the initial and final conditions are the same.
We can manipulate the given thermochemical equations to obtain the desired reaction:
1. Reverse the first equation:
2 NH3(g) → N2(g) + 3 H2(g), and change the sign of ΔH to +91.8 kJ.
2. Double the second equation:
2 C(graphite) + 4 H2(g) → 2 CH4(g), and double ΔH to -149.8 kJ.
3. Reverse the third equation:
2 HCN(g) → H2(g) + 2 C(graphite) + N2(g), and change the sign of ΔH to -270.3 kJ.
Now, we can add the modified reactions together to obtain the overall reaction:
2 NH3(g) + 2 C(graphite) + 4 H2(g) → 2 HCN(g) + 2 H2(g) + 2 C(graphite) + N2(g)
Simplifying, we get:
2 NH3(g) + 4 H2(g) → 2 HCN(g) + 2 H2(g) + N2(g)
Now, we can cancel out the repeating compounds:
2 NH3(g) + 2 H2(g) → 2 HCN(g) + N2(g)
Adding all the ΔH values together, we get:
ΔH = (+91.8 kJ) + (-149.8 kJ) + (-270.3 kJ) = -328.3 kJ
Therefore, the heat of reaction at constant pressure for the given reaction is -328.3 kJ.