Question

The initial internal energy of a mug of coffee is known to be 168 Btu. The initial coffee temperature is approximately 200 F. The room temperature is 70 F. Time passes and the final amount of internal energy in the coffee is 68 Btu. How much heat flowed from the coffee to the room?

Answer 1

100Btu

Step-by-step explanation:

According to the First law of thermodynamics:

ΔQ = W + ΔU

Where,

ΔQ is the heat change

W is the amount of work done

ΔU is change in internal energy

Since, there is no work done on the system as heat is just passing from coffee mug to surroundings, So, W = 0

Thus,

Net heat change = change in internal energy.

Change in internal energy =
`U_f-U_i=(68-168)\ Btu=-100\ Btu`

Thus,

ΔQ = -100 Btu (negative sign indicates release of heat)

So,

Heat flown to the room = 100Btu