The reaction below shows the decomposition of sodium azide into sodium metal and nitrogen gas.
2NaN3(s)-> 2Na(s) + 3N2(s)
An unknown amount of sodium azide (NaN3) reacts and produces 744 mL of nitrogen gas. What mass of sodium metal is produced?

0.51g

Explanation:

Given parameters:

Volume of nitrogen gas  = 744mL

Unknown:

Mass of sodium metal produced = ?

Solution:

Let us assume that the gas, nitrogen was collected at STP which is the standard temperature and pressure, we can easily find its number of moles.

            Number of moles  =

since the gas volume given is 744mL = 0.744mL

   Therefore input the variables;  

         Number of moles  =   = 0.03moles

Now that we know the number of moles of the gas, let us revisit the reaction equation:

      2NaN₃   →   2Na    +  3N₂

It good to ensure that the reaction is balanced;

         3 mole of nitrogen gas is produced with 2 moles of Na

        0.03 mole of nitrogen gas will be produce with  = 0.02mole

So;

       Using;

                    mass  = number of moles x molar mass

let us solve for the mass of Na;

                   molar mass of Na = 23g/mol

                  mass  = 0.02 x 23  = 0.51g

option c: 1605.1 kj

the balanced chemical reaction for combustion of methane is as follows:

here, enthalpy formation of is -74.7 kj/mol, 0 kj/mol, -393.5 kj/mol and -241.82 kj/mol respectively.

the heat released or can be calculated as follow:

putting the values,

thus, heat released by combustion of 1 mol of methane is 802.54 kj/mol. thus, for 2 mol, heat released will be:

therefore, heat released by the combustion of 2 mol of methane is 1605.1 kj.