Given the following data, calculate the enthalpy change for the reaction
S(s)+ O2(g)->SO2(g)
S(s)+(3/2)O2(g)->SO3(g) H=-395.2 kJ
2SO2(g)+ O2(g)->2SO3(g) H=-198.2 kJ
To calculate the enthalpy change for the reaction S(s) + O2(g) -> SO2(g), we can use the given data for two other reactions and apply Hess's Law.
Step 1: Flip the equation and change the sign of the enthalpy change:
SO2(g) -> S(s) + O2(g) ΔH = ?
Step 2: Multiply the second equation by -2:
-2(SO2(g) + O2(g) -> 2SO3(g)) ΔH = 2 * (-198.2 kJ) = -396.4 kJ
Step 3: Multiply the first equation by 2:
2(S(s) + (3/2)O2(g) -> SO3(g)) ΔH = 2 * (-395.2 kJ) = -790.4 kJ
Step 4: Rearrange the equations to match the desired reaction:
S(s) -> S(s) + (3/2)O2(g) ΔH = -790.4 kJ
SO2(g) -> S(s) + O2(g) ΔH = ?
Step 5: Add the equations together:
2(S(s) + (3/2)O2(g) -> SO3(g)) + -2(SO2(g) + O2(g) -> 2SO3(g)) = -790.4 kJ + -396.4 kJ
Step 6: Simplify the equation:
-1580.8 kJ + 792.8 kJ = -788 kJ
Therefore, the enthalpy change for the reaction S(s) + O2(g) -> SO2(g) is -788 kJ.
To calculate the enthalpy change for the reaction S(s) + O2(g) -> SO2(g), you need to use the Hess's Law of heat summation. Hess's Law states that if a reaction can be expressed as the sum of multiple reactions, then the enthalpy change of the overall reaction is equal to the sum of the enthalpy changes of the individual reactions.
In this case, we have two given reactions:
1) S(s) + (3/2)O2(g) -> SO3(g) with a given enthalpy change H = -395.2 kJ
2) 2SO2(g) + O2(g) -> 2SO3(g) with a given enthalpy change H = -198.2 kJ
To derive the desired reaction, we need to manipulate these reactions to cancel out the common species, which is SO3(g). Here's how:
Multiply the first reaction by 2:
2(S(s) + (3/2)O2(g) -> SO3(g)) with enthalpy change (2 x -395.2 kJ) = -790.4 kJ
Now, add the two reactions together:
2(S(s) + (3/2)O2(g) -> SO3(g)) + (2SO2(g) + O2(g) -> 2SO3(g))
Cancelling out the common species (SO3(g)), we get:
2S(s) + 2(3/2)O2(g) + 2SO2(g) + O2(g) -> 2SO2(g) + 2SO3(g)
Simplifying, we get:
2S(s) + 4O2(g) + 2SO2(g) -> 2SO2(g) + 2SO3(g)
The enthalpy change of the reaction is simply the sum of the enthalpy changes of the manipulated reactions:
(-790.4 kJ) + (-198.2 kJ) = -988.6 kJ
Therefore, the enthalpy change for the reaction S(s) + O2(g) -> SO2(g) is -988.6 kJ.
deltaHrxn = (n*DH products) - (n*DH reactants)
DH = delta H.