Question

A student dissolves 10. g of sodium carbonate in a coffee cup calorimeter and measures an increase in water temperature of 8.0 degrees. Assuming the coffee cup contained 175 g of pure water, what is the ΔH of solution for this reaction in kJ/mol?

Answer 1

Specific heat of water= 4.184 j/gm.deg.c

the heat released during the adiabatic heat exchange is transferred to water and this heat = mass of water*change in temperature * specific heat of water= 10*4.184*(-8) = -335 joules

this heat is due to dissolution of 10 gm of sodium carbonate ( Na2CO3) in water

atomic weights ( g/mole): Na= 23, C= 12 and O=16

molar mass of Na2CO3= 2*23+12+3*16= 106 g/mole

moles of Na2CO3= mass of Na2CO3/ molar mass= 10/106 =0.094 moles

deltaH of solution = -335/0.094 j/mole = -3551 j/mole= -3.551 KJ/mole