In modeling this process, assume the passage of sufficient time for the broken egg to return to its initial temperature. What is the origin of the heat transfer of part (e)?

An egg, initially at rest, is dropped onto a concrete surface and breaks. With the egg treated as the system,

(a) What is the sign of W?

(b) What is the sign of

(c) What is

(d) What is

(e) What is the sign of Q?


W is positive – work is done by gravity on the egg

a. is negative – the potential energy of the egg decreases when it falls.

b. is zero – the egg starts out with zero velocity (and therefore zero kinetic energy, relative to the earth) and ends with zero velocity.

c. If the egg returns to its original temperature, then for the egg is zero. U is a state function, so if the egg starts and ends at the same T and P (and there are no chemical changes in the egg), then U doesn’t change.

d. Q is negative – the work done on the egg is converted to heat when the egg (irreversibly) breaks on the pavement. If the egg returns to its original temperature, this heat must all flow into the concrete, so that = Q + W = 0.

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