Reacting Amounts Using Equations Flashcards

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Note: We may include questions that have multiple correct answers. It's useful to remember specific examples to understand these concepts better.

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What does a balanced symbol equation tell you about the amounts of substances in a reaction?

It shows the ratio of moles of each reactant and product that take part in the reaction.

In a balanced symbol equation, what do the big numbers in front of the formulas show?

They show how many moles of each substance react or are made, in the simplest whole-number ratio.

Before doing reacting amount calculations, what must you always check about the chemical equation?

You must check that the equation is balanced, with the same number of each type of atom on both sides.

What simple formula links mass, relative formula mass (Mr) and moles in reacting amount calculations?

Number of moles = mass (in g) ÷ relative formula mass (Mr).

State the three main steps to find the mass of a product from the mass of a reactant using a balanced equation.

First, change the known mass into moles. Next, use the mole ratio from the equation to find the moles of the other substance. Finally, change those moles back into a mass.

In the reaction 2H2 + O2 → 2H2O, what is the ratio of moles of hydrogen gas to moles of water made?

The ratio is 2 moles of hydrogen gas to 2 moles of water, which can be simplified to 1:1.

In the equation N2 + 3H2 → 2NH3, how many moles of ammonia are made when 3 moles of hydrogen react fully?

2 moles of ammonia are made.

What is meant by the 'limiting reactant' in a reaction?

It is the reactant that is used up first, so it stops the reaction and limits how much product can form.

What does it mean if a reactant is 'in excess' in a reacting amount calculation?

It means there is more of that reactant than is needed to react with the other reactant, so some will be left over.

How can you decide which reactant is limiting using a balanced equation and the numbers of moles of each reactant?

Work out the moles of each reactant. Use the balanced equation to find the ratio they should react in. The reactant you do not have enough of to match this ratio is the limiting reactant.

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