what is the answer?

Question

A 2.50 g sample of powdered zinc is added to 100.0 mL of a 2.00 M aqueous solution of hydrobromic acid in a calorimeter. The total heat capacity of the calorimeter and solution is 448 J/K. The observed increase in temperature is 21.1 K at a constant pressure of one bar. Calculate the standard enthalpy of reaction using these data.

Zn(s)+2HBr(aq)⟶ZnBr2(aq)+H2(g)



Δ𝐻∘rxn=

Answer 1

1st, you have to establish which of the reactants is limiting (it rates to be the Zn as the thermal properties of left over Zn are not given): 2.5 g/ 65.38 g/mole : ( .1 liter)(2 mole/liter HCl) is < 1:2 (the stoichiometric mix)

We can use the equation -n_ZnΔH= C_calΔT so ΔH = -C_calΔT/n_Zn (energy released goes into heating the solution and the calorimeter.

ΔH = -448 J/K *(21.1°C)/(2.5 g/65.38 g/mole) = 2.47 x 10⁵ J/mole of Zn which is the same as the reaction statement.

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