1a. When a solid dissolves in water, heat may be evolved or absorbed. The heat of...

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.
ΔH_dissolution = 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.
ΔH_dissolution = kJ/mol

This is all the information the question gives me.

Solutions

Expert Solution

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

queen_honey_blossom answered 10 months ago

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