What is the wavelength of light emitted when an electron in a hydrogen atom undergoes a transition from energy level n = 6 to level n = 1? (c  = 3.00  × 108 m/s, h =  6.63 × 10–34 J·s, RH  =  2.179 × 10–18 J)

A red laser pointer emits light at a wavelength of 488 nm. If the laser emits 7.5 × 10–4 J of energy per second in the form of visible radiation, how many photons per second are emitted from the laser?

What is the minimum mass of ice at 0.0 °C that must be added to 1.00 kg of water to cool the water from 28.0 °C to 12.0 °C? (Heat of fusion = 333 J/g; specific heat capacities: ice = 2.06 J/g⋅K, liquid water = 4.184 J/g⋅K)

At constant pressure and 25°C, what is ΔrH° for the following reaction 2C2H6(g) + 7O2(g) → 4CO2(g) + H2O(l) if the complete consumption of 22.7 g of C2H6 liberates –1178 kJ of heat energy?

What quantity, in moles, of hydrogen is consumed when 179.6 kJ of energy is evolved from the combustion of a mixture of H2(g) and O2(g)? H2(g) + O2(g)  →  H2O(l); ΔrH° = –285.8 kJ/mol-rxn

Calculate ΔU of a gas for a process in which the gas absorbs 45 J of heat and does 11 J of work by expanding.

What is the formal charge of the oxygen atom in the Lewis structure for cyanate shown below?  

What is the formal charge on the carbon atom in CO?

A light emitting diode (L.E.D.) emits photons with an energy of J. What is the energy per mole of photons emitted? ​

If a cordless phone operates at a frequency of 9.00 × 108 s–1, what is the wavelength of this radiation?