Calculate the volume of oxygen gas required to react completely with 10g of magnesium to make magnesium oxide

Explanation:

The idea here is that chemical reactions must obey the Law of Mass Conservation, which states that when a chemical reaction takes place, the total mass of the reactants must be equal to the total mass of the products.

In your case, magnesium metal and oxygen gas are the reactants and magnesium oxide is the product.

2

Mg

(

s

)

+

O

2

(

g

)

→

2

MgO

(

s

)

You know that

10.0 g

of magnesium take part in this reaction and that

16.6 g

of magnesium oxide are produced.

You can say that the difference between the mass of the product and the total mass of the reactants, i.e. the mass of magnesium and the mass of oxygen gas, will give you the mass of oxygen gas that took part in the reaction.

m

Mg

+

m

O

2

=

m

MgO

−−−−−−−−−−−−−−−−−−

→

the Law of Mass Conservation

You will thus have

m

O

2

=

m

MgO

−

m

Mg

m

O

2

=

16.6 g

−

10.0 g

=

6.6 g

−−−−

The answer is rounded to one decimal place

c, liquids evaporate, creating a gas

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.