sum of reactants = sum of products
11.9 g + 5.10 g = 17.0 g
23.8 g + 10.2 g = 34.0 g
The law of conservation of mass tells you that mass can neither be created nor destroyed. In a chemical equation, the total mass of the reactants must equal the total mass of the products. Based on this, calculate the missing values in the table below.
Table 1 |
|||
| Iron reacted | Oxygen gas reacted | Iron (III) oxide produced | |
| Experiment 1 | 11.9 g | 5.10 g | |
| Experiment 2 | 10.2 g | 34.0 g | |
What would you do if you needed to calculate an amount of product or reactant but hadn’t been provided all the other masses? Well, you need to know how the chemicals relate to each other in a balanced equation! Once you know the coefficients, the molar ratios will allow you to convert between any two chemicals that are in the reaction.
Let’s summarize how you solved the problem. You read the problem to identify which two chemicals were being related to each other. You looked to the balanced chemical equation to find the mole ratio between the two chemicals. Then, you set up your dimensional analysis and used the form of the mole ratio that “cancelled out” the unit you did not want in order to convert to your desired unit.
Since you are so familiar with the synthesis reaction for iron(III) oxide now, work on a couple more practice problems. Don’t be intimidated by numbers that are not integers. Remember, moles don’t need to be whole numbers.
4 Fe + 3 O2 → 2 Fe2O3
