Question

3) Methane can be combusted in the presence of oxygen to form carbon dioxide and water. The reaction isshown below:CH4 + 2 O₂ CO₂ + 2 H₂Oa) How many CH, molecules are in 2.2 g of CH₂?b) If the density of water is 997 kg / m³, how many moles of oxygen are needed to produce 500 mL ofwater?c) How many atoms of hydrogen will be used to produced 40.5 g of CO₂?Edit: a) How many CH4, molecules are in 2.2 g of CH4?

Answer 1

a) The first step is finding the molar mass of CH4 to convert the mass given (2.2 g) into moles.

MM = 12.0 + 4*1.0 = 16 g/mol

If 16 g = 1 mole, we can calculate how many moles are 2.2 g by doing the following:

16 g ---- 1 mole

2.2 g ----- x mole

$\frac{16}{2.2}=\frac{1}{x}\Rightarrow16x=2.2\Rightarrow x=0.1375\text{ }mol$

Now we use Avogadro's number to find how many molecules are present in this amount of moles of methane (CH4).

Avogadro's number is 6.0*10^23 molecules/mol

1 mole ---- 6.0*10^23 molecules

0.1375 mole ---- y molecules

$\frac{1}{0.1375}=\frac{6.0*10^{23}}{y}\Rightarrow y=0.1375*6.0*10^{23}\text{ }\Rightarrow y=8.3*10^{22}\text{ molecules}$

There are 8.3*10^22 molecules in 2.2 g of CH4.