Please check my work energy required to raise temp by 10degthanks

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SUMMARY

The discussion centers on calculating the work required to heat 1 liter of water by 10 ºC using a mechanical egg beater powered by a descending mass. The user correctly determines that 1 liter of water corresponds to 55.5 moles, requiring 417915.0 J of energy to achieve the desired temperature increase. The mechanical work formula |work| = mg(x_f - x_0) is applied to find that the mass must descend 42.6 meters to supply this energy. However, there is a critical error in the user's calculation of energy, as noted by other participants, indicating a misunderstanding of orders of magnitude.

PREREQUISITES
  • Understanding of thermodynamics, specifically heat capacity.
  • Familiarity with the concept of mechanical work and its formula.
  • Basic knowledge of moles and molar mass calculations.
  • Ability to convert between joules and kilojoules.
NEXT STEPS
  • Review the principles of heat capacity and its application in thermodynamic calculations.
  • Study the mechanical work formula and its components in detail.
  • Learn about orders of magnitude and their importance in scientific calculations.
  • Practice converting energy units, specifically between joules and kilojoules.
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Students studying physics or engineering, educators teaching thermodynamics, and anyone interested in understanding the relationship between mechanical work and thermal energy transfer.

Dars
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Homework Statement



You want to heat 1 L of water by 10 ºC, and so you heat it with a mechanical egg beater that is powered by a 1 kg mass on a rope over a pulley. How far does the mass have to descend to supply enough work for heating the water?

Homework Equations


|work| = mg(x_f - x_0)
C_P (liquid water) = 75.3JK^-1mol^1


The Attempt at a Solution


I first asked myself how much energy does it take to increase the temp of 1kg of water by 10degC.
Heat capacity of water (above) is the energy required to heat 1 mol of water by 1deg.
So I first determined how many moles of water i have:

1L = 1kg = 1000g * (1mol/18.01g) = 55.5mol of liquid water

Therefore 55.5mol *75.3JK^-1mol^1 = 4179.15J/K * 10K = 417915.0J

So it requires 417915.0J to raise the temp of 1kg water by 10degC.

This is the work required also because work is also in joules, --energy.

Then i used the formula for mechanical work to determine the value for delta x.

|work| = mg(x_f - x_0)

417915.0J(1kJ/10000J) = 1kg(9.81m/s/s)(x_f) (i got ride of x_0 because I set scale so that x_0 = 0)

x_f = 42.6m

So the mass has to descend through 42.6m in order to heat 1kg of liquid water by 10 degC.

Is this correct or if not please help..thanks a lot. I also have some other questions about the problem but i don't want to ask until i know if my answer is correct...thank you again
 
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Dars said:
1L = 1kg = 1000g * (1mol/18.01g) = 55.5mol of liquid water
Correct.
Dars said:
Therefore 55.5mol *75.3JK^-1mol^1 = 4179.15J/K * 10K = 417915.0J
"WORNG." Ten x four thousand equals four hundred thousand?
Dars said:
Then i used the formula for mechanical work to determine the value for delta x.
|work| = mg(x_f - x_0)
417915.0J(1kJ/10000J) = 1kg(9.81m/s/s)(x_f) (i got ride of x_0 because I set scale so that x_0 = 0)
x_f = 42.6m
So the mass has to descend through 42.6m in order to heat 1kg of liquid water by 10 degC.
"Four kilometers." You need to pay attention to decimal "orders of magnitude."
 

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