By using the three steps given below (either as shown or in the reverse order), the mass of a substance involved in a chemical reaction can be related to the volume of a gas produced or consumed in the reaction.
Calculate amount in moles of known substance.
Relate n(known) to n(unknown)
Use the coefficients of the balanced equation to relate any pair of substances in the balanced equation.
To solve for n(unknown substance), first divide n(known substance) by its coefficient in the balanced equation and then multiply the result by the coefficient of the unknown.
Calculate V(unknown) using from n(unknown)
The molar volume is the volume occupied by 1 mol of gas at a specified temperature.
It is useful to set up a plan for solving a problem before doing calculations. Analysis of problems in this way shows that the steps are similar in problems that may look, from the words, to be quite different.
Calculate amount in moles of known substance.
This can be calculated from a given mass (m) if the formula of the substance is known, so that the molar mass (M) can be calculated.
| n = | m |
| M |
Relate n(known) to n(unknown)
Use the coefficients of the balanced equation to relate any pair of substances in the balanced equation.
| n(known substance) | = | n(unknown substance) |
| a | b | |
| a and b are coefficients | ||
To solve for n(unknown substance), first divide n(known substance) by its coefficient in the balanced equation and then multiply the result by the coefficient of the unknown.
Calculate V(unknown) using from n(unknown)
The molar volume is the volume occupied by 1 mol of gas at a specified temperature.
V(gas) = n × molar volume
= mol × mol-1
= mol × mol-1
It is useful to set up a plan for solving a problem before doing calculations. Analysis of problems in this way shows that the steps are similar in problems that may look, from the words, to be quite different.
| Known |
|
| ||||||||||
| m(A) |  | n(A) | | n(B) | ||||||||
| mass A | Step 1 | amount A | Step 2 | amount B |
| V = n(B) × molar volume | Unknown |
| V(B) |