Two grams of water are sealed in a rigid container; then the water is vaporized by heating. 955 cal of heat is needed for vaporization. What is the change in internal energy of the water? Answer in units of J

Explanation:

According to the first law of thermodynamics:

Here is the change in the internal energy of the system, Q is the supplied heat to the system and W is the work done by the system. The work done by the system is defined as:

Where P is the presion and is the volume change. The volume remains constant, since the water are sealed in a rigid container:

So, the change in internal energy of the water is:

1 cal is equal to 4.186 J, so:

heat the gas and measure the pressure

no. dot product   =0 when vecs at right angles