Question

Magnesium is added to 250 ml of HCl(aq) in a 187g tin container. Calculate the enthalpy change if the temperature of water increases 8.9 degrees Celsius.

Answer 1

The reaction:

Mg(s) + 2HCl(aq) --> MgCl2(aq) + H2(g)

V = 250 mL,

m = 187 g of tin container

Find HRxn

HRxn = Qtotal = Qwater + Qcontainer

assume D = 1 g/mL for water

Qwater = mass of water * Cp water * (Tf-Ti) = 250*4.184 * (8.9) = 9309.4 J

Cp tin = 0.21 J/g°C

Qcontainer = mass of container * Cp tin * (Tf-Ti) = 187 * 0.21 * 8.9 = 349.503 J

HRxn = Qtotal = Qwater + Qcontainer

HRxn = Qtotal = 9309.4 + 349.503 J = 9658.903 J

HRxn = - 9658.903 J It is negative, since Mg + HCl --> exothermic (release in energy, s system loses Energy)