Enthalpy questions?
Given this enthalpy change
MgCl₂(s)---->Mg²⁺(g) +2Cl⁻(g)
ΔH∅ =+2490KJ/mol
Mg2+(g)----> Mg²⁻ (aq)
ΔH∅ =-1920KJ/mol
Cl⁻(g)---->Cl⁻(aq)
ΔH∅ =-360KJ/mol
What is the Enthalpy change in KJ/mol for following process
MgCl₂(s)---->MgCl₂(aq)
please show the workings
To find the enthalpy change for the process MgCl₂(s) -> MgCl₂(aq), we can use Hess's Law, which states that the enthalpy change of a reaction is the same regardless of the route taken.
Hess's Law allows us to manipulate the given reactions and their enthalpy changes to obtain the desired reaction and its enthalpy change.
Here are the steps to find the enthalpy change for the process MgCl₂(s) -> MgCl₂(aq):
Step 1: Reverse the second reaction:
2Cl⁻(aq) -> Cl⁻(g)
Since we reversed the reaction, we also need to change the sign of the enthalpy change:
ΔH₁ = +360 KJ/mol
Step 2: Reverse the third reaction:
Mg²⁻(aq) -> Mg2+(g)
Again, we change the sign of the enthalpy change:
ΔH₂ = -(-1920) KJ/mol = +1920 KJ/mol
Step 3: Add the reversed reactions together, cancelling out the Cl⁻(g) and Mg²⁻(aq) species:
(Mg²⁺(g) + 2Cl⁻(g)) + (Cl⁻(g) + Mg²⁻(aq)) -> MgCl₂(aq)
Simplifying the equation:
Mg²⁺(g) + Cl⁻(g) -> MgCl₂(aq)
Step 4: Add the enthalpy changes of the reactions together:
ΔH_total = ΔH₁ + ΔH₂ = +360 KJ/mol + 1920 KJ/mol = 2280 KJ/mol
Therefore, the enthalpy change for the process MgCl₂(s) -> MgCl₂(aq) is 2280 KJ/mol.
To find the enthalpy change for the process MgCl₂(s) → MgCl₂(aq), we can break it down into the sum of the enthalpy changes for individual steps.
Step 1: MgCl₂(s) → Mg²⁺(g) + 2Cl⁻(g) (given: ΔH∅ = +2490 KJ/mol)
This step represents the dissolution of MgCl₂(s) into its constituent ions in the gas phase. Since the given enthalpy change is for the formation of 1 mol of MgCl₂, it represents the enthalpy change for 1 mol of Mg²⁺(g) and 2 mol of Cl⁻(g).
Step 2: Mg²⁺(g) → Mg²⁺(aq) (given: ΔH∅ = -1920 KJ/mol)
This step represents the solvation of Mg²⁺ ions in water to form Mg²⁺(aq). The given enthalpy change is for 1 mol of Mg²⁺(g) transforming into 1 mol of Mg²⁺(aq).
Step 3: Cl⁻(g) → Cl⁻(aq) (given: ΔH∅ = -360 KJ/mol)
This step represents the solvation of Cl⁻ ions in water to form Cl⁻(aq). The given enthalpy change is for 1 mol of Cl⁻(g) transforming into 1 mol of Cl⁻(aq).
Now, we can sum up the enthalpy changes for each step to find the overall enthalpy change for the process:
ΔH = step 1 + step 2 + step 3
ΔH = (+2490 KJ/mol) + (-1920 KJ/mol) + (-360 KJ/mol)
ΔH = 210 KJ/mol
Therefore, the enthalpy change for the process MgCl₂(s) → MgCl₂(aq) is 210 KJ/mol.