At 25 C the following heats of reaction are known:
2CIf (g)+ O2(g) -> CL2O (g) + f2O
Delta H rxn= 167.4 kj/mol
2CIf3(g) + 2O2 (g)-> Cl2O(g) + 3F2O(g)
Delta H rxn= 341.4
2F2(g) + O2(g) -> 2F2O(g)
Delta H rxn= -43.4kj/mol
at the temperature, use Hess's Law to calculate delta H rxn for the reaction
CIF (g) + F2 (g) -> CIF3 (g)
Hess law confuses me
Hess's Law allows us to calculate the enthalpy change of a reaction by using other known enthalpy changes. To apply Hess's Law, we need to manipulate and combine the given reactions in a way that cancels out the desired reaction and allows us to find its enthalpy change.
Let's go step by step to calculate ΔH_rxn for the reaction:
1. We can start by using the first reaction and reverse it to match the desired reaction:
Reverse: CL2O (g) + F2O -> 2CIF (g) + O2 (g)
ΔH_1 = -167.4 kJ/mol
2. Multiplied by the stoichiometric coefficients to balance the equation:
Multiply by 2: 2CL2O (g) + 2F2O -> 4CIF (g) + 2O2 (g)
ΔH_1 = -334.8 kJ/mol
3. Now, let's use the second reaction, which contains CIF3:
Reverse and multiply by 2: Cl2O (g) + 3F2O (g) -> 2CIF3 (g) + 2O2 (g)
ΔH_2 = -341.4 kJ/mol
4. Lastly, we can use the given reaction with CIF and F2:
CIF (g) + F2 (g) -> CIF3 (g)
ΔH_3 = -ΔH_rxn (desired value, to be calculated)
5. Add the manipulated equations together to cancel out the intermediates:
Equation 1 + Equation 2 + Equation 3 gives us:
-334.8 kJ/mol + (-341.4 kJ/mol) + ΔH_3 = 0
6. Simplify the equation and solve for ΔH_rxn:
ΔH_3 = 334.8 kJ/mol + 341.4 kJ/mol
ΔH_3 = 676.2 kJ/mol
Therefore, the ΔH_rxn for the reaction CIF (g) + F2 (g) -> CIF3 (g) is 676.2 kJ/mol.
Hess's Law is a principle in thermochemistry that states that the enthalpy change for a chemical reaction is independent of the pathway taken, as long as the initial and final conditions remain the same. In other words, the overall enthalpy change for a reaction can be calculated by combining the enthalpy changes of a series of other reactions.
To calculate the ΔH_rxn for the reaction CIF(g) + F2(g) → CIF3(g) using Hess's Law, we need to find a series of reactions that, when combined, can yield the desired reaction. Here's a step-by-step guide:
Step 1: Write the given reaction and the known reactions:
Given reaction: CIF(g) + F2(g) → CIF3(g)
Known reactions:
1. 2CIF(g) + O2(g) → CL2O(g) + F2O(g) (ΔH_rxn = 167.4 kJ/mol)
2. 2CIF3(g) + 2O2(g) → CL2O(g) + 3F2O(g) (ΔH_rxn = 341.4 kJ/mol)
3. 2F2(g) + O2(g) → 2F2O(g) (ΔH_rxn = -43.4 kJ/mol)
Step 2: Manipulate the known reactions to obtain the desired reaction:
First, reverse reaction 1 to form CIF(g) on the left side:
CL2O(g) + F2O(g) → 2CIF(g) + O2(g) (ΔH_rxn = -167.4 kJ/mol)
Next, multiply reaction 1 by 2 to balance the number of CIF molecules:
2CL2O(g) + 2F2O(g) → 4CIF(g) + 2O2(g)
Finally, combine the above equation with reaction 2 and reaction 3 to obtain the desired reaction:
2CIF3(g) + 2O2(g) → CL2O(g) + 3F2O(g)
2F2(g) + O2(g) → 2F2O(g)
CIF(g) + F2(g) → CIF3(g)
Step 3: Add the ΔH_rxn values for the individual reactions:
ΔH_rxn = ΔH_rxn1 + ΔH_rxn2 + ΔH_rxn3
Note: When manipulating reactions, the ΔH_rxn values are multiplied or reversed accordingly.
Now, substitute the ΔH_rxn values from the given reactions:
ΔH_rxn = (-167.4 kJ/mol) + (341.4 kJ/mol) + (-43.4 kJ/mol)
Step 4: Calculate the ΔH_rxn for the desired reaction:
ΔH_rxn = 130.6 kJ/mol
Therefore, the ΔH_rxn for the reaction CIF(g) + F2(g) → CIF3(g) is 130.6 kJ/mol.
I hope this explanation helps you understand how to apply Hess's Law to calculate the enthalpy change for a reaction. Let me know if you have any further questions or if there's anything else I can assist you with!