Thermochemistry

Question

The molar enthalpy of solution for ammonium chloride is +14.8 kJ/mol. What is the final temperature observed when 20.0g of ammonium chloride is added to 125 mL of water at 20.0°C . Give only the quantity in °C Do not give the unit.

Answer 1

Since we are given the molar enthalpy in kJ/mol, we need to first find how many moles of NH₄Cl we have.

20.0 g NH₄Cl x 1 mol/53.5 g = 0.3738 moles

q = mC∆T

q = heat = 0.3738 mol x 14.8 kJ/mol = 5.53 kJ = 5530 J

m = mass = 125 ml x 1g/ml = 125 g + 20 g = 145 g (assuming a density of 1g/ml for water)

C = specific heat = 4.184 J/g/degree (assuming the C for solution is same as C for water)

∆T = change in temperature = ?

Solving for ∆T:

∆T = q / (m)(C) = 5530 J / (145 g)(4.184 J/g/degree)

∆T = 9.12 (without units)