Question #8bcb2
1 Answer
The reaction releases 7.71 L of
Explanation:
Here are the steps to follow:

First, write the balanced equation for the reaction.

Use the molar mass to convert grams of
#"Mg"# to moles of#"Mg"# . 
Use the molar ratio between
#"Mg"# and#"H"_2# to get the moles of#"H"_2# . 
Finally, use the molar volume to convert moles of
#"H"_2# to litres of#"H"_2#
.
Let’s see how this works.
1. The balanced equation is
2. Calculate the moles of
3. Calculate the moles of
The balanced equation tells us that
4. Calculate the volume of
STP is defined as 0 °C and 1 bar.
Under these conditions, the volume of 1 mol of an ideal gas is 22.711 L.
To convert moles to litres at STP, we use the relation
So,
Notice how we always write the conversion factors so that the units cancel to give the desired units for the answer.