Question

Heat is added to an open pan of water at 100.0°c, vaporizing the water. the expanding steam that results does 43.0 kj of work, and the internal energy of the system increases by 604 kj. how much energy is transferred to the system as heat?

Answer 1

Heat = change in internal energy + Work done The internal energy of a system = heat added and mechanical work done by the system, i.e. U = Q + W rearranging the formula above, will give us: Q = deltaU + W 
Q = U - W = 604 kJ - 43.0 kJ = 561,000 J would be the answer.

Answer 2

Answer:

Heat transferred to the gas is given as

Q = 647 kJ

Explanation:

As per first law of thermodynamics we know that

$Q = \Delta U + W$

now here we know that

change in internal energy of the gas is

$\Delta U = 604 kJ$

Also the steam expands so we will have

$W = 43 kJ$

since volume increases to here work is done by the gas

now from above equation the heat given to the system is

$Q = 604 + 43 = 647 kJ$