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Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

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BuyFindarrow_forward

Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

When 0.850 g of Mg was burned in oxygen in a constant-volume calorimeter, 25.4 kJ of energy as heat was evolved. The calorimeter was in an insulated container with 750. g of water at an initial temperature of 18.6 °C. The heat capacity of the bomb in the calorimeter is 820. J/K.

  1. (a) Calculate ΔU for the oxidation of Mg (in kJ/mol Mg).
  2. (b) What will be the final temperature of the water and the bomb calorimeter in this experiment?

(a)

Interpretation Introduction

Interpretation:

The internal energy for the oxidation of Mg has to be determined

Concept Introduction:

Heat energy required to raise the temperature of 1g of substance by 1K..Energy gained or lost can be calculated using the below equation.

  q=C×m×ΔT

Where, q= energy gained or lost for a given mass of substance (m), C =specific heat capacity, ΔT= change in temperature.

Sum of all energies transferred as heat in the system

  qr + qbomb +qwater=0

Explanation

Mass of magnesium is 0.850g

Molar mass of Mg is 24.305g/mol

So, number of moles of magnesium is:

0.850g24.305 g/mol =0.0349moles of Mg

For -25

(b)

Interpretation Introduction

Interpretation:

The change in internal energy in the system has to be calculated.

Concept Introduction:

Standard enthalpy of the reaction,ΔrHo, is the change in enthalpy that happens when matter is transformed by a given chemical reaction, when all reactants and products are in their standard states.

Enthalpy change for the reaction ΔrH0=ΣnΔfH0(products)-ΣnΔfH0(reactants)

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