   # On a cold day, you can warm your hands with a “heat pad,” a device that uses the oxidation of iron to produce energy as heat. 4 Fe(s) + 3 O 2 (g) → 2 Fe 2 O 3 (s) A hand warmer uses the oxidation of iron as a source of thermal energy. What mass of iron is needed to supply the energy required to warm 15 mL of water ( d = 1.00 g/mL) from 23 °C to 37 °C? ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640

#### Solutions

Chapter
Section ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640
Chapter 5, Problem 100IL
Textbook Problem
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## On a cold day, you can warm your hands with a “heat pad,” a device that uses the oxidation of iron to produce energy as heat.4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) A hand warmer uses the oxidation of iron as a source of thermal energy.What mass of iron is needed to supply the energy required to warm 15 mL of water (d = 1.00 g/mL) from 23 °C to 37 °C?

Interpretation Introduction

Interpretation:

The required amount of Fe to warm 15mL of water 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 of the reaction,ΔrH, is the change in enthalpy that happens when matter is transformed by a given chemical reaction

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.

The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one gram of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.

ΔrH0=ΣnΔfH0(products)-ΣnΔfH0(reactants)

### Explanation of Solution

Given,

ΔfH Of Fe=0

ΔfH Of oxygen = 0

ΔfH Of Fe2O3=-822.2kJ/mol

ΔrH0=ΣnΔfH0(products)-ΣnΔfH0(reactants)

ΔrH= (2mol×-822.2kJ/mol)- (0)

ΔrH=-1644kJ

Heat required to warm 15mL water

Specific capacity of heat of iron is 0

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