A sample of 0.75 KCL is added to 35 g of H2O in a calorimeter and stirred until dissolved, the temperature of the solution decreases from 24.8 to 23.6 what is the enthalpy of solution expressed in kJ / mole KCL?
Note that you need to spell chemistry correctly.
The heat of solution which is the heat lost when KCl dissolves, is given by the decrease in temperature of the water as
q = mass H2O x specific heat H2O x (Tfinal-Tinitial)
That q is for 0.75g which is 0.75g/molar mass KCl = mols KCl.
Then q/mol KCl = gives you J/mol and change that to kJ/mol. Post your work if you get stuck.
17.449kJ/mol
To find the enthalpy of solution expressed in kJ/mol KCl, we need to use the equation:
ΔH = q / n
where ΔH is the enthalpy change of the solution, q is the heat absorbed or released, and n is the number of moles of solute dissolved.
First, let's calculate the heat absorbed or released (q). We can use the equation:
q = m * C * ΔT
where q is the heat, m is the mass of the water, C is the specific heat capacity of water, and ΔT is the change in temperature.
Given:
Mass of water (m) = 35 g
Specific heat capacity of water (C) = 4.184 J/g°C (or 4.184 J/g K because 1°C is equivalent to 1 K)
Change in temperature (ΔT) = 23.6°C - 24.8°C = -1.2°C (Note: Remember to use the same unit for temperature in the equation, so we'll convert to Kelvin)
Converting the mass and temperature units:
Mass of water (m) = 35 g
Change in temperature (ΔT) = -1.2 K (since 1°C = 1 K)
Calculating q using the equation:
q = (35 g) * (4.184 J/g K) * (-1.2 K)
q = -178.32 J
Now, let's calculate the number of moles of KCl (n). We can use the equation:
n = mass / molar mass
where n is the number of moles, mass is the mass of the solute, and molar mass is the molar mass of KCl.
Given:
Mass of KCl (solute) = 0.75 g
Molar mass of KCl = 74.55 g/mol
Calculating n:
n = 0.75 g / 74.55 g/mol
n = 0.01006 mol
Now we can calculate the enthalpy change (ΔH) using the equation:
ΔH = q / n
ΔH = -178.32 J / 0.01006 mol
ΔH = -17,727.43 J/mol
To express ΔH in kJ/mol, divide by 1000:
ΔH = -17,727.43 J/mol / 1000
ΔH ≈ -17.73 kJ/mol
Therefore, the enthalpy of solution expressed in kJ/mol KCl is approximately -17.73 kJ/mol.