Chapter 20, Problem 24PS

### Chemistry & Chemical Reactivity

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

Chapter
Section

### Chemistry & Chemical Reactivity

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

# Calculate the energy used, in kilojoules, to power a 100-watt lightbulb continuously over a 24-hour period. How much coal would have to be burned to provide this quantity of energy, assuming that the enthalpy of combustion of coal is 33 kJ/g and the power plant has an efficiency of 35%? (Electrical energy for home use is measured in kilowatt hours (kW-h). One watt is defined as 1 J/s, and 1 kW-h is the quantity of energy transferred when 1000 watt is dispensed over a 1.0-hour period.)

Interpretation Introduction

Interpretation:

It should be determined that the energy in kilo joules used to power a 100watt light bulb continuously over an 24 hour period and the quantity of coal would have to be burned to provide this quantity of energy.

Concept introduction:

• Enthalpy of combustion is the energy released by a combustion reaction between hydrocarbons, oxygen and heat source.
• Enthalpy of formation is the heat released or absorbed in a chemical reaction at constant temperature when simple substances combine into a more complex substance.
• 1watt=1J/s1kwh=3600kJ
• 1kWh is the quantity of energy transferred when 1000watt is dispensed over a 1.0hourperiod
Explanation

Given,

The amount of energy to power 100â€‰wattâ€‰ light bulb continuously over 24 hour period can be calculated as follows,

â€‚Â 100â€‰wâ€‰Ã—â€‰24â€‰hrâ€‰â€‰â€‰â€‰â€‰=â€‰â€‰â€‰â€‰2400â€‰whâ€‰â€‰=â€‰â€‰â€‰2.4â€‰kwhconvertingâ€‰â€‰thisâ€‰â€‰intoâ€‰â€‰kJ,2.4â€‰Ã—3600â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰â€‰=â€‰â€‰8640â€‰kJ

The enthalpy of combustion of coal is 33â€‰KJ/g

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