A mixture of H2 and water vapor is present in a closed vessel at 20°C. The total pressure of the system is 755. 0 mmHg. Partial pressure of water vapor at 20°C equals 17. 5 mmHg. What is the partial pressure of H2? mmHg.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

1 is the answer to this problem

the answer is c.the valence of the atoms combine .

yes the answer is total mass in unchanged   : )