Question

A solution containing 2.610 g of CuSO_4.5H_2O (molar mass 249.7 g mol^-1) is completely reacted with excess Zn metal in a constant pressure calorimeter, according to: Cu^2 + + Zn rightarrow Cu + Zn^2 + (a) Determine delta H for the reaction as written above if a temperature change of 4.319 K is measured in the reaction mixture. Assume that the combined heat capacity of the calorimeter and solution is 526.37 J K^-1. (b) Is the enthalpy change determined in (i) the standard enthalpy change (delta H) for the reaction?

Answer 1

a) $\large \Delta$​H = q_p = C_p$\large \Delta$T where Cp = 526.37J/K and $\large \Delta$​T = 4.319 K

= 526.37 J/K x 4.319 K = 2273.4 J

Number of moles of CuSO4.5 H2O = given mass/molar mass = 2.610g/249 g/mol = 0.0105 mol

Molar enthalpy, $\large \Delta$​H = 2273.4/0.0105 J/mol = 216.5 kJ/mol

b) standard enthalpy change is the enthalpy measured at 1 bar pressure and 298 K temperature. So the enthalpy is not the standard enthlpy change of the reaction.