General Chemistry problems.

1. Natural gas burns in air to form carbon dioxide and water, releasing heat.
CH4(g)+O2(g)→CO2(g)+H2O(g)
ΔHorxn = -802.3 kJ
   1. What minimum mass of CH4 is required to heat 45.0g of water by 20.0∘C? (Assume 100% heating efficiency.) (For water,Cs= 4.18 J/g∘C).


2. A cylinder with a moving piston expands from an initial volume of 0.100L against an external pressure of 2.90atm . The expansion does 247J of work on the surroundings. What is the final volume of the cylinder?


3. Manganese reacts with hydrochloric acid to produce manganese(II) chloride and hydrogen gas.
Mn(s)+2HCl(aq) → MnCl2(aq)+H2(g)
   3. When 0.605g Mn is combined with enough hydrochloric acid to make 100.0 mL of solution in           a coffee-cup calorimeter, all of the Mn reacts, raising the temperature of the solution from 23.6∘C to 29.5∘C.
Find ΔHrxn for the reaction as written. (Assume that the specific heat capacity of the solution is 4.18 J/g∘C and the density is 1.00 g/mL.)


4. How much energy (in J) is contained in 1.00 mole of 641nm photons?