Enthalpy change is the a. amount of energy absorbed or lost by a system as heat during a process at constant pressure.
b. entropy change of a system at constant pressure.
c. pressure change of a system at constant temperature.
d. temperature change of a system at constant pressure.

Which statement about the stamps is correct?

Determine the wavelength of the light absorbed when an electron in a hydrogen atom makes a transition from an orbital in the n=3 level to an orbital in the n=7 level.

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?