In: Chemistry
1a. When a solid dissolves in water, heat may be evolved or
absorbed. The heat of dissolution
(dissolving) can be determined using a coffee cup
calorimeter.
In the laboratory a general chemistry student finds that when
1.33 g of CaBr2(s) are
dissolved in 103.70 g of water, the temperature of
the solution increases from 24.23
to 25.85 °C.
Based on the student's observation, calculate the enthalpy of
dissolution of CaBr2(s) in
kJ/mol.
Assume the specific heat of the solution is equal to the specific
heat of water.
ΔHdissolution = kJ/mol
1b. In the laboratory a general chemistry student finds that
when 21.18 g of
Cs2SO4(s) are dissolved in
112.90 g of water, the temperature of the solution
drops from 24.64 to
21.92 °C.
Based on the student's observation, calculate the enthalpy of
dissolution of Cs2SO4(s) in
kJ/mol.
Assume the specific heat of the solution is equal to the specific
heat of water.
ΔHdissolution = kJ/mol
This is all the information the question gives me.
Question 1A
Let us consider the following water
Q = mc∆T
Q = heat energy (Joules, J), m = mass of a substance (g)
c = specific heat (units J/g∙°C), ∆ is a symbol meaning "the change in"
∆T = change in temperature (°C Celcius)
Q = ? m = 103.70 g + 1.33 g = 105.03 g ∆T = 25.85 °C - 24.23 °C = 1.62 °C
c = 4.184 J/g∙°C
Q = 105.03 g x 4.184 J/g∙°C x 1.62 °C = 711.90 Joules
Q = 711.90 Joules or 0.7119 Kilo Joules
Moles of CuBr2 = 1.33 g /223.37 g/mol = 0.00595 Moles
enthalpy of dissolution of CaBr2 = 0.71190 Kilo Joules / 0.00595 Moles = 119.64 Kilo Joules / mole
Hence the enthalpy of dissolution of CaBr2 is 119.64 Kilo Joules / mole
Question 1 b
Let us use the same formula
Q = ? m = 112.9 g + 21.18 g = 134.08 g ∆T = 24.64 °C - 21.92 °C = 2.72 °C
c = 4.184 J/g∙°C
Q = 134.08 g x 4.184 J/g∙°C x 2.72 °C = 1525.89 Joules
Q = 1525.89 Joules or 1.525 Kilo Joules
Moles of Cs2SO4 = 21.18 g /361.8735 g/mol = 0.05852 Moles
enthalpy of dissolution of Cs2SO4 = 1.525 Kilo Joules / 0.05852 Moles = 26.059 Kilo Joules / mole
Hence the enthalpy of dissolution of Cs2SO4 is 26.059 Kilo Joules / mole