A quantity of 2.30 × 10 2 mL of 0.800 M HNO 3 is mixed with 2.30 × 10 2 mL of 0.

Question

A quantity of

2.30

×

102 mL of 0.800 M

HNO3

is mixed with

2.30

×

102 mL of 0.400 M

Ba(OH)2

in a constant-pressure calorimeter of negligible heat capacity. The initial temperature of both solutions is the same at

18.46

°

C.

The heat of neutralization when 1.00 mol of

HNO3

reacts with

0.500 mol

Ba(OH)2

is

56.2 kJ/mol.

Assume that the densities and specific heats of the solution are the same as for water (

1.00 g/mL

and

4.184 J/g

respectively). What is the final temperature of the solution?

Enter your answer in the provided box. The enthalpy of combustion of benzoic acid (C6H5COOH) is commonly used as the standard for calibrating constant-volume bomb calorimeters; its value has been accurately determined to be 3226.7 kJ/mol. When 3.2315 g of benzoic acid are burned in a calorimeter, the temperature rises from 20.84°C to 26.67°C. What is the heat capacity of the bomb? (Assume that the quantity of water surrounding the bomb is exactly 2250 g.)

Explanation / Answer

For the neutralization reaction,

dH = mCpdT

let Tf be the final temperature of the mixture

56.2 x 0.5 = (2.3 x 10^2 + 2.3 x 10^2)(4.184)(Tf - 18.46)

Tf = 18.475 oC

For the second set of data for benzoic acid

moles of benzoic acid = 3.2315/122 = 0.0265 mol

dT = 26.67 - 20.84 = 5.83 oC

So,

heat capacity of bomb = 3226.7 x 0.0265/5.83

                                    = 14.667 kJ/oC

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