Question

Zinc metal reacts with hydrochloric acid solution according to the reaction: zn(s) + 2 hcl(aq)  zncl2(aq) + h2(g). suppose 0.103 g of zn(s) is combined with 50.0 ml of hcl solution in a styrofoam cup calorimeter and all the zn(s) reacts. the temperature of the solution rises from 22.5 0 c to 23.7 0
c. the solution has a density of 1.0 g/ml and a specific heat capacity of 4.18 j/g- 0

c.

a. find ∆hr for this reaction in units of kj/mol.

b. what would be the work of the system in joules when one mole of zn reacts?

c. what would be the work of the system in joules when 0.103 g of zn reacts?

Answer 1

Mass of Zn  = 0.103 g

Volume of HCl (V) = 50.0 ml

Density of solution (D) = 1.00 g/ml

Mass of HCl = D*V = 1.00 g/ml * 50.0 ml = 50.0 g

initial temp T1 = 22.5 C

Final temp T2 = 23.7 C

specific heat c = 4.18 J/g C

The heat (Q) required to raise the temp is given as:

Q = mcΔT = mc(T2-T1)

  = (0.103+50)g * 4.18 J/g C * (23.7-22.5) C = 251.3 J = 0.2513 kJ

To find ΔH in kJ/mol

# moles of Zn = mass of Zn/Atomic mass = 0.103/65.39 = 0.00158 moles

a) ΔH = 0.2513 kJ/0.00158 moles = 159.05 kJ/mol

b) A calorimeter is an isolated system where there is no exchange of heat/energy.

Work done is given as: W = PΔV

since ΔV = 0, as the volume remains constant

W = 0