. When a 28.7 g sample of KI dissolves in 60.0 g of water in a calorimeter, the temperature drops from 27.2oC to 13.2 oC . Calculate ΔH for the process.
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
That is dH for the process BUT you probably want per mol KI. q/mol KI = ?
To calculate ΔH for the process, we need to use the equation:
ΔH = q / n
Where:
- ΔH = enthalpy change
- q = heat transferred
- n = number of moles of the substance
First, we need to calculate the heat transferred (q).
q = m * c * ΔT
Where:
- q = heat transferred
- m = mass of the solution
- c = specific heat capacity of water
- ΔT = change in temperature
Given values:
m = 60.0 g (mass of water)
c = 4.18 J/g°C (specific heat capacity of water)
ΔT = (13.2 - 27.2) oC = -14.0 oC (change in temperature)
Substituting these values into the equation, we get:
q = 60.0 g * 4.18 J/g°C * (-14.0 oC)
q = -35,294.4 J
Next, we need to calculate the number of moles of KI.
The molar mass of KI is:
K = 39.1 g/mol
I = 126.9 g/mol
Molar mass of KI = 39.1 g/mol + 126.9 g/mol = 166.0 g/mol
n = mass / molar mass
n = 28.7 g / 166.0 g/mol
n = 0.1733 mol
Finally, substitute the values of q and n into the equation to calculate ΔH:
ΔH = q / n
ΔH = (-35,294.4 J) / (0.1733 mol)
ΔH = -203,538 J/mol
Therefore, the enthalpy change (ΔH) for the process is approximately -203,538 J/mol.
To calculate the enthalpy change (ΔH) for the dissolving process, we need to use the formula:
ΔH = q / mol
Where q is the heat transferred during the process, and mol is the number of moles of solute (in this case, KI).
To find q, we need to use the equation:
q = m × c × ΔT
Where m is the mass of the solvent (in this case, water), c is the specific heat capacity of water, and ΔT is the change in temperature.
First, we need to calculate the heat transferred (q):
q = m × c × ΔT
q = 60.0 g × 4.18 J/g·°C × (13.2 °C - 27.2 °C)
q = -8949 J
Next, we need to calculate the number of moles of KI dissolved:
To do this, we divide the mass of KI by its molar mass.
molar mass of KI = (molar mass of K) + (molar mass of I)
= 39.10 g/mol + 126.90 g/mol
= 166.00 g/mol
Number of moles of KI = mass of KI / molar mass of KI
= 28.7 g / 166.00 g/mol
= 0.173 moles
Now, we can calculate the enthalpy change (ΔH) using the formula:
ΔH = q / mol
ΔH = -8949 J / 0.173 moles
ΔH = -51717 J/mol
Therefore, the enthalpy change (ΔH) for the dissolving process is -51717 J/mol.