The chemical equation below shows the burning of magnesium (Mg) with oxygen (O2) to form magnesium oxide (MgO).

2Mg + O2 Right arrow. 2MgO

Niven wants to calculate the mass of MgO that is produced by the burning of 28.0 g of Mg. What is the first step in Niven's calculation?

Balance the chemical equation.

Convert grams of Mg to moles.

Determine whether heat is given off by this reaction.

Find the number of Mg atoms in the sample.

The correct answer is Option-B (Convert grams of Mg to moles)

Explanation:

In stoichiometry problems the first step is always to balance the given unbalanced chemical equation. In our case the given equation is already balanced hence, we looked for the second step.

As Niven wants to calculate the mass of MgO (which is the product) with respect to Mg (reactant) hence here comes another important rule. In such cases if one wants to compare masses of two reactants or reactant product. or product product then one should first convert the given mass into moles, also the same conversion for the second mass and then compare the moles and at last convert the moles back into mass. So, the flow chart should be like,

Mass (Mg) → Moles (Mg) : (MgO) Moles ← (MgO) Mass

After finding moles following step take place,

Moles (MgO) → Mass (MgO)

B. Convert grams to moles

Explanation:

Always the first step to do in any assignment like this if they already gave you mass of sth