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## Homework Statement

A restaurant refrigerator has a coefficient of performance of 4.5. If the temperature in the kitchen outside the refrigerator is 28^\circ C, what is the lowest temperature that could be obtained inside the refrigerator if it were ideal?

## Homework Equations

According to textbook, COP=TL/(TH-TL)

## The Attempt at a Solution

So wouldn't it be 4.5=TL/(28-TL)? And I got 23 degrees celsius but that's wrong...So I don't know where I'm wrong.

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## Homework Statement

What is the change in entropy of 3.00 m^3 of water at 0 C when it is frozen to ice at 0 C?

## Homework Equations

So I'm thinking the problem is saying what the change in entropy when water changes from solid to liquid....

If so, then change in entropy = Q/T = (m*heat of fusing)/T (kelvin)

## The Attempt at a Solution

I'm stuck on on to convert 3.00 m^3 into mass... would that be the same as 3kg? I know 1kg=1L= either 1cm^3 or 1m^3?

----- If it's equal to 3kg...then change in entropy would be 3kg*333000J/kg / (273K) ???

still didn't get the right answer as 3660J/K

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## Homework Statement

A 120 g insulated aluminum cup at 19 C is filled with 150 g of water at 55 C. After a few minutes, equilibrium is reached.

Estimate the total change in entropy.

## Homework Equations

I found final temperture to be 50 degrees, but I'm stuck on how to calculate the

*total*change in entropy...

Totaly change in entrophy = change in entrophy of aluminum cup + change in entrophy of the water

## The Attempt at a Solution

S for al cup = Q/T= 900*.120kg*(50-19)/(273+50K) = 10.4

S for water = Q/T = 4186*.150*(55-50)/(273+50K) = 9.72

total S = 10.4+9.72=20.1 J/K

But it says that's wrong...

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