   # 9.98 Hydrogen combines with oxygen in fuel cells according to the thermochemical equation 2H 2 ( g ) + O 2 ( g ) → 2H 2 O ( g ) Δ H ° = - 571.7 kJ Suppose that you are working with a firm that is using hydrogen fuel cells to power satellites. The satellite requires 4 .0 × 1 0 5 kJ of energy during its useful lifetime to stabilize its orbit. Describe how you would determine the mass of hydrogen you would need in your fuel cells for this particular satellite. ### Chemistry for Engineering Students

3rd Edition
Lawrence S. Brown + 1 other
Publisher: Cengage Learning
ISBN: 9781285199023

#### Solutions ### Chemistry for Engineering Students

3rd Edition
Lawrence S. Brown + 1 other
Publisher: Cengage Learning
ISBN: 9781285199023
Chapter 9, Problem 9.92PAE
Textbook Problem
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## 9.98 Hydrogen combines with oxygen in fuel cells according to the thermochemical equation   2H 2 ( g ) + O 2 ( g ) → 2H 2 O ( g ) Δ H ° = -571.7 kJ Suppose that you are working with a firm that is using hydrogen fuel cells to power satellites. The satellite requires 4 .0 × 1 0 5 kJ of energy during its useful lifetime to stabilize its orbit. Describe how you would determine the mass of hydrogen you would need in your fuel cells for this particular satellite.

Interpretation Introduction

Interpretation:

The mass of hydrogen to be used in the fuel cell in order to power the satellite should be calculated.

Concept introduction:

• Thermochemical equations depict the enthalpy change (ΔH)of a chemical reaction in terms of the reaction stoichiometry.
• Chemical reactions proceed with the absorption (endothermic) or evolution (exothermic) of heat.
• Enthalpy change is negative for an exothermic reaction and positive for an endothermic reaction.

### Explanation of Solution

Given: Thermochemical equation: 2H2(g)+O2(g) 2H2O(g)

Enthalpy change (ΔH) = -571.7 kJ

Energy required by the satellite = 4.0×105 kJ

Calculation:

Step I: Calculate the number for moles of hydrogen required for the given satellite energy

As per the stoichiometry of the thermochemical equation:

571.7 kJ of energy is released by 2 moles of H2

Moles of H2 required for to produce an energy of 4

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