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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: apinkhighlighter on December 23, 2018, 01:26:46 PM

Title: Heat Transfer Question
Post by: apinkhighlighter on December 23, 2018, 01:26:46 PM
In my class, we've started thermodynamics and I think I'm having trouble understanding the equation to calculate heat transfer (
q = mCpΔT ). I've supplied the problem below as well as my work. I was just wondering if someone on here would mind checking my work.

Question: How much heat is required to raise the temperature of 754 g of water from 32.9°C to 88.6°C?

Mathematical Answer:

q = 754(4.184J/g°C)55.7°C
q = (754)(4.184)
q = (3,154.746)(55.7)
q = 175,718.7952J

My answer is 175,718.7952 joules.

Textual Answer
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I first identified my 'm', the mass of the water at 754 grams. Then, I identified the specific heat capacity of water, which is 4.184. After I identified both the mass of the water and the heat capacity of water, I found the difference between my two temperatures, which will give me a positive 'q' value in the end. The difference between my two temperatures, 32.9°C and 88.6°C was 55.7°C. I plugged in all of my numbers into the equation ( q = mCpΔT ) and multiplied from left to right. My final answer was 175,718.7952 joules.

Thank you for reading and for your time!
Title: Re: Heat Transfer Question
Post by: Borek on December 23, 2018, 02:33:20 PM
 Looks more or less ok. You just don't have enough information to supply the answer with so many significant digits.
Title: Re: Heat Transfer Question
Post by: Enthalpy on December 24, 2018, 09:54:25 AM
The 4184 J/kg/K apply to pure water around +20°C and 1atm. At +30°C it's rather 4180 J/kg/K and at +90°C +4205 J/kg/K
https://www.engineeringtoolbox.com/specific-heat-capacity-water-d_660.html
that's probably at the saturation pressure in that table, but at 30-90°C it makes a small difference.

Measuring a temperature (meaningfully!) to 0.1K isn't completely trivial neither, so a fourth place in the answer would be overstretched.