A 4.50 g sample of LiCl at 250 C dissolves in 25.0 ml of water also at 25.0 C.? The final equilibrium temp of the resulting solution is 60.8 C. What is the enthalpy of solution, deltaHs, of LiCl expressed in kilojoules per mole.
To find the enthalpy of solution, deltaHs, of LiCl (lithium chloride), we can use the equation:
deltaHs = Q / n
Where:
- deltaHs is the enthalpy of solution (in kilojoules per mole),
- Q is the heat absorbed or released during the dissolution process (in joules),
- n is the number of moles of solute.
To solve this problem, we need to follow these steps:
1. Calculate the heat absorbed or released (Q) during the dissolution process.
2. Determine the number of moles (n) of LiCl in the 4.50 g sample.
3. Convert the units and calculate the enthalpy of solution (deltaHs).
Let's start by calculating the heat absorbed or released during the dissolution process:
Q = mcΔT
Where:
- Q is the heat (in joules),
- m is the mass of the water (in grams),
- c is the specific heat capacity of water (4.18 J/g°C),
- ΔT is the change in temperature (in °C).
We need to calculate the mass of water we have. Since the density of water is 1.00 g/ml, we can convert the volume of water to grams:
mass of water = volume of water * density of water
mass of water = 25.0 ml * 1.00 g/ml
...calculating...
mass of water = 25.0 g
Now, we can calculate the heat absorbed or released during the dissolution process (Q):
Q = mcΔT
Q = (25.0 g) * (4.18 J/g°C) * (60.8 - 25.0) °C
...calculating...
Q ≈ 40460 J
Next, we need to determine the number of moles of LiCl in the 4.50 g sample. We can use the molar mass of LiCl which is 42.39 g/mol.
moles of LiCl = mass of LiCl / molar mass of LiCl
moles of LiCl = 4.50 g / 42.39 g/mol
...calculating...
moles of LiCl ≈ 0.1064 mol
Finally, we can calculate the enthalpy of solution (deltaHs) by converting the units:
deltaHs = Q / n
deltaHs = (40460 J) / (0.1064 mol)
...calculating...
deltaHs ≈ 380,433 J/mol
To convert the enthalpy of solution to kilojoules per mole:
deltaHs (kJ/mol) = deltaHs (J/mol) / 1000
deltaHs (kJ/mol) ≈ 380.43 kJ/mol
Therefore, the enthalpy of solution (deltaHs) of LiCl is approximately 380.43 kJ/mol.