Embedded Files
Scaling Chemical Equations
Scaling Chemical Equations
Since we can find balanced equations, we can actually scale the information in them up or down to find out exactly how much of a different reactant or product we should get from a reaction. The numbers we use are based on the ratio found in the chemical equations we make and this process of using ratios is known as stoichiometry. For example:
The ratio will always be 2 magnesium and 1 oxygen gas forming 2 magnesium oxide for this equation! That means:
4 magnesium atoms and 2 oxygen gas molecules make 4 magnesium oxide molecules.
12 magnesium atoms and 6 oxygen gas molecules make 12 magnesium oxide molecules.
5,000 magnesium atoms and 2,500 oxygen gas molecules make 5,000 magnesium oxide molecules.
2 moles of magnesium and 2 moles of oxygen gas make 4 moles of magnesium oxide.
23 moles of magnesium and 11.5 moles of oxygen gas make 23 moles of magnesium oxide.
Moles are an amount of molecules so the ratio stays true for both units!
If a chemical equation has an energy term, that term will scale just like the compounds and atoms do within the equation. For example, a formula with a term that contains the amount of energy released is:
2 H2 + O2 -> 2 H2O + 570 kJ/mol
If we had 10 moles of H2 then the energy term would become 2850 since the formula is scaled to 5 times as much as it was before.
Limiting Factors
Limiting Factors
In the real world, we often don’t get to use perfect ratios. Whatever reactant we run out of first is known as the limiting reactant, or what would stop the reaction from continuing. To tell what's limiting you need to take the amounts you have for each reactant in a chemical equation then divide each of these by their coefficient. Whichever amount is the smallest after that is the one that's limiting the reaction:
H + O -> H2O
Balanced would be:
2 H + O -> H2O
Oxygen is limiting here since we run out of it first! We need 2 Hs for every O!
8 H + 3 O -> 3 H2O (We would have 2 extra Hs, meaning we run out of O first and O is the limiting reactant)
After finding a limiting reactant, whatever is left over is known as an excess reactant. These reactants remain in the area even after everything that reacts becomes a product, allowing us to filter this extra stuff out or use it for a different reaction later.
Additional Resources
Additional Resources
Interesting Links
Interesting Links
Page updated
Report abuse