9 Hydrogen chloride gas is highly soluble in water When diss

9. Hydrogen chloride gas is highly soluble in water. When dissolved in water the solution is called hydrochloric acid. When 10.o g of hydrogen chloride is dissolved in 1oo.o g of water in a calorimeter at 25.0°C the temperature rises to 69.5°C a. Is this process exothermic or endothermic? Justify your answer. b. How much heat was given off by the creation of this particular solution? Assume that the specific heat of the HCl solution is the same as that of water and that the density is still about 1 g/mL. Also, remember to use the total mass of the contents of the calorimeter in calculating the heat of the solution c. What is the molar heat of solution for hydrogen chloride?

Solution

a) The dissolution process gives off heat and hence, the temperature of the system (HCl + water) rises. Since HCl gives off heat (i.e, releases heat), the reaction is exothermic.

b) Mass of the solution = mass of HCl + mass of water = 10.0 g + 100.0 g = 110.0 g.

The specific heat of the solution is the same as the specific heat of water, i.e, 4.18 J/g.ºC.

Heat gained by the solution = (mass of the contents of the calorimeter)*(specific heat of the solution)*(change in temperature of the solution) = (110.0 g)*(4.18 J/g.ºC)*(69.5 – 25.0)ºC = 20461.1 J.

Since HCl gave off heat which increased the temperature of the water in the calorimeter, hence, the heat given off by HCl = -20461.1 J (ans).

c) Molar mass of HCl = (1.008 + 35.453) g/mol = 36.453 g/mol.

Mole(s) of HCl corresponding to 10.0 g HCl = (10.0 g)/(36.453 g/mol) = 0.2743 mole.

Molar heat of solution of HCl = (heat released by HCl)/(moles of HCl) = (-20461.1 J)/(0.2743 mole) = -74593.87532 J/mol = (-74593.87532 J/mol)*(1 kJ/1000 J) = -74.59387532 kJ/mol -74.59 kJ/mol (ans).