Which of the following is produced when two or more elements combine in a chemical reaction?

The enthalpy of formation of water is -285.8 kj/mol. what can be inferred from this statement?

3. how much energy in joules is required to evaporate .0005 kg of liquid ammonia to vapor at the same temperature? 4. how much energy ( in megajoules ) is given up by .75 kg of water at 0c when it freezes to form ice at 0c? 5. explain how heat works between and at critical temperatures?

What substance has a mass of 9.5g and volume of 2.1cm^3