Chemistry For engineers: thermodynamics

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SUMMARY

The discussion focuses on calculating the amount of coal needed to power a 75-W reading lamp for two hours, given a reasonable efficiency of 30% for converting chemical energy to electrical energy via combustion. The user correctly identifies the need to use the enthalpy of combustion for graphite and applies the equation E = time × power to determine energy requirements. By factoring in the efficiency and converting the resulting mass of carbon from grams to pounds, the user successfully arrives at the solution.

PREREQUISITES
  • Understanding of thermodynamics principles, specifically combustion reactions.
  • Familiarity with the concept of enthalpy and its application in chemical reactions.
  • Basic knowledge of energy calculations, including the relationship between power, time, and energy.
  • Ability to convert units, specifically from grams to pounds.
NEXT STEPS
  • Research the enthalpy of combustion for various fuels, including graphite.
  • Learn about energy efficiency in combustion processes and its implications.
  • Explore advanced thermodynamic equations related to energy conversion.
  • Study unit conversion techniques for mass and energy in chemical engineering contexts.
USEFUL FOR

Chemical engineers, energy analysts, and students studying thermodynamics who are looking to understand energy conversion and efficiency in combustion processes.

nboyd1
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[SOLVED] Chemistry For engineers: thermodynamics

I was given a question: Reasonable efficiency for converting chemical energy to electrical energy via combustion is 30%. Calculate the how many pounds of coal must be burned to run your reading lamp for two hours. Atypical reading lamp has a 75-W bulb. Assume that coal is pure graphite. ( 1W=1J/s)

Yo be honest this is nothing like the examples given in class of even in the book. I'm not sure what where to even begin, which equation to use. My intial instinct was it should be a heat capacity equation, but I don't know how the other information relates or how to calculate that given this information.
 
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Start by writing the equation for the combustion of carbon (graphite to be exact). You will need to look up the enthalpy of the reaction.
 
chemisttree said:
Start by writing the equation for the combustion of carbon (graphite to be exact). You will need to look up the enthalpy of the reaction.

i think i got the answer. i found delta h for the reaction then used E=time*power, the divind by 30 percent and setting up a proportion with weight of carbon to get the number of grams and finally converted to pounds
 

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