Nitrogen oxides undergo many interesting reactions in the environment and in industry. Given the following information, calculate H for the overall equation: 2 NO2(g) + 1/2 O2(g) = N2O5(s).
2 NO(g) + 3/2 O2(g) = N2O5(s), H = -223.7 kJ
NO(g) + 1/2 O2(g) = NO2(g), H = -57.1 kJ
Multiply equation 2 by 2 and reverse it.
Add in equation 1.
That will give you what you want.
-109.5
To calculate the enthalpy change (ΔH) for the overall equation: 2 NO2(g) + 1/2 O2(g) = N2O5(s), we can use Hess's Law.
Hess's Law states that if a reaction can be expressed as a sum of two or more reactions, the ΔH for the overall reaction is equal to the sum of the ΔH values for the individual reactions.
Given the following information:
1) 2 NO(g) + 3/2 O2(g) = N2O5(s), H = -223.7 kJ
2) NO(g) + 1/2 O2(g) = NO2(g), H = -57.1 kJ
We need to manipulate the equations to match the overall equation, and then we can add the enthalpy changes together:
First, calculate the enthalpy change for the reverse of equation 2:
NO2(g) = NO(g) + 1/2 O2(g), H = +57.1 kJ
Next, multiply equation 2 by 2 to match the number of moles of NO2 in the overall equation:
2 NO2(g) = 2 NO(g) + O2(g)
Now we can add the enthalpy changes together:
2 NO2(g) + 1/2 O2(g) = N2O5(s)
(2 NO(g) + O2(g)) + (NO2(g) + 1/2 O2(g)) = N2O5(s)
2 NO(g) + O2(g) + NO2(g) + 1/2 O2(g) = N2O5(s)
The enthalpy change for the overall equation is the sum of the enthalpy changes for the individual reactions:
ΔH = (-223.7 kJ) + (+57.1 kJ) = -166.6 kJ
Therefore, the enthalpy change (H) for the overall equation is -166.6 kJ.
To calculate the enthalpy change (H) for the overall equation, you can use the concept of Hess's Law. According to Hess's Law, the overall enthalpy change of a reaction is equal to the sum of the enthalpy changes of the individual reactions involved.
In this case, we have three reactions:
1) 2 NO(g) + 3/2 O2(g) = N2O5(s), H = -223.7 kJ (Equation 1)
2) NO(g) + 1/2 O2(g) = NO2(g), H = -57.1 kJ (Equation 2)
3) 2 NO2(g) + 1/2 O2(g) = N2O5(s) (Overall Equation)
To find the enthalpy change for the overall equation, you need to manipulate equations 1 and 2 by multiplying or reversing them if necessary, so that their reactants and products match those in the overall equation.
Multiply Equation 1 by 2:
4 NO(g) + 3 O2(g) = 2 N2O5(s) (Equation 3)
Now, reverse Equation 2:
NO2(g) = NO(g) + 1/2 O2(g) (Equation 4)
Notice that Equation 4 now has the same reactants and products as Equation 3, but with opposite signs for the enthalpy change.
Add Equation 4 to Equation 3 to cancel out NO(g):
4 NO(g) + 3 O2(g) + NO2(g) = 2 N2O5(s) + NO(g) + 1/2 O2(g)
Simplifying the equation:
3 NO(g) + 3 O2(g) = 2 N2O5(s) + 1/2 O2(g)
This equation represents the overall equation, which means the enthalpy change (H) for the overall equation is the sum of the enthalpy changes of the individual reactions:
H(overall) = H(3 NO(g) + 3 O2(g) = 2 N2O5(s) + 1/2 O2(g))
Hence, to calculate H(overall), add the enthalpy changes for each reaction:
H(overall) = H(Equation 3) + H(Equation 4)
H(overall) = -223.7 kJ + (-57.1 kJ)
H(overall) = -280.8 kJ
Therefore, the enthalpy change (H) for the overall equation is -280.8 kJ.