The reaction between chlorine and hydrogen occurs in the presence of sunlight at room temperature while that between fluorine and hydrogen occurs in the dark and at low temperatures. Explain why.

When a chemist collects hydrogen gas over water, she ends up with a mixture of hydrogen and water vapor in her collecting bottle. if the pressure in the collecting bottle is 97.1 kilopascals and the vapor pressure of the water is 3.2 kilopascals, what is the partial pressure of the hydrogen?