Converting Calories to Joules: Uncovering the Correct Conversion Formula

  • Context: High School 
  • Thread starter Thread starter Quarlep
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    Joule Mass
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Discussion Overview

The discussion revolves around the conversion of calories to joules, specifically addressing the correct conversion formula and the units involved. Participants explore the relationship between calories, joules, and specific heat, with a focus on the implications of using different units in calculations.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant proposes that 1 calorie is equivalent to 4.2 J/g°C, leading to a calculation of 8400000 g m²/s².
  • Another participant clarifies that 1 calorie is actually 4.2 J, noting the distinction between calorie and specific heat of water.
  • A participant attempts to derive a relationship between heat (Q), mass (m), and work (W) using the equations Q=mcT and W=mgh, expressing confusion over unit consistency.
  • It is suggested that the specific heat should be used per kilogram instead of per gram to resolve unit discrepancies, indicating that 4200 J/(kg·°C) is the appropriate conversion.

Areas of Agreement / Disagreement

Participants express differing views on the correct interpretation of units and conversion factors, indicating that multiple competing perspectives remain without a clear consensus on the issue.

Contextual Notes

There are unresolved assumptions regarding the definitions of calories and joules, as well as the context in which specific heat is applied. The discussion highlights potential confusion stemming from mixing units of grams and kilograms.

Quarlep
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Lets suppose we have 2000 kcal and we want to translate it joule.
1 calorie is 4,2 J/gC isn't it so I think it will be 8400000 g m^2/s^2 But my teacher says its 8400000 kg m^2/s^2
Which one is true
Thanks
 
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Note: Here (4,2 J/gC) J is joule g is grams and C is celsius
 
Quarlep said:
1 calorie is 4,2 J/gC isn't it

No, 1 cal = 4.2 J (to one decimal place).

You're thinking of the specific heat of water, which is 4.2 J/(g·°C) = 1 cal/(g·°C).
 
Then let me clear Q=mcT and W=mgh so If we takes m we get Q/cT=W/gh If we write the unit form cal cal^-1 g C^-1 C we get g which it grams
and the other side kg m^2 s^-2 s^2 m^-1 m^-1 then we get kg.It does not match.and I think its a problem
 
You're getting grams for the m from the first equation because you're using the specific heat per gram. Use the specific heat per kilogram instead: 4200 J/(kg·°C).
 
Thanks I understan it
 

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