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33 votes
2. How much heat in kilojoules has to be removed from 225g of water to lower its temperature from 25.0oC to 10.0oC?

User Vgru
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1 Answer

25 votes
25 votes

Answer:

-14.1 kJ

Explanation:

We need the specific heat of water, which is 4.184 J/g-K. It means that 4.184 Joules of energy will raise 1 gram of water by 1 degree Kelvin. It also means that removing 4.184 Joules of energy will lower the temperature of 1 gram of water by 1 degree Kelvin.

We want to lower the temperature by 15 degrees C (-15C). That is also -15K. We have 225 grams of water.

This can be used in the equation q = mc(T2 - T1),

where q is the heat, or energy, m is the mass, c is the specific heat, and (T2-T1) is the temperature change, in Kelvin.

q = mc(T2 - T1)

q = (225g)(4.184 J/g-K)(10K - 25K)

q = (225g)(4.184 J/g-K)(-15K)

q = -14121 J or -14.1 kJ

It is negative because heat is leaving the system.

User Mike Hildner
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