CHEMISTRY
posted by Persia .
1).What is the pressure in a 1.5 L vessel containing 0.25 moles of O2 if the temperature is 37 degrees celcius?
2).The molar mass of MgCO3 is 84g/mole. How many moles are in 12.60g of MgCO3?

#1. Use PV = nRT. Don't forget to change C to Kelvin. Kelvin = C + 273.
#2. # mol = g/molar mass. 
Would you please further explain the steps to sloving #2?
Thanks 
There isn't anything to explain.
# mols = grams/molar mass. Plug in grams from the problem (12.6) and molar mass from the problem (84) and divide on your calculator. I get something like 0.15 or so
# mols = 12.6/84 = ??. If you prefer to do these by the dimensional method, then
# mols = 12.6 g x (1 mol/84g) = ?? mols. (Note how the unit we don't want (grams) cancel and the unit we want to keep (mols) doesn't cancel. We have converted, using a factor, grams to mols. 
What is the pressure in a 1.5 L vessel containing 0.25 moles of O2 if the temperature is 37oC? (R, the universal gas constant, is 0.082 L atm / mole K.)