If 200 grams of water is to be heated from 24 degrees to 100 degrees to make a cup of tea, how much heat must be added

Question

If 200 grams of water is to be heated from 24 degrees to 100 degrees to make a cup of tea, how much heat must be added

Answer 1

The specific heat for water is 4.184 J/g/deg

The equation relating heat (energy) to mass and temperature is q = mC∆T where q = heat energy; m = mass; C = specific heat; and ∆T = the change in temperature.

 

q = (200g)(4.184 J/g/deg)(76 degrees)

q = 63,597 J = 63.6 kJ

NOTE:  the units of temperature (ºC or ºK) doesn't matter because you are using a ∆T, or a change in temperature, and so a change of 76ºC is the same as a change of 76ºK, etc.

Answer 2

q = mcΔT

 

q = heat added

 

m = mass of the water = 200 g = 0.200 kg

 

c = specific heat of water (look up in your chemistry book)

 

ΔT = temperature rise = 100º - 24° (you need to state the units, e.g. °C, °F, etc.)

 

Plug in the numbers using the correct units for the temperature change.