# How to calculate the amount of substances product produces from the masses and amounts of starting materials?

Calculate the amount of carbon dioxide formed when we burn 1 mole of carbon in the presence of 16 g of dioxygen. $$\ce{C + O2 -> CO2}$$

1 mole of carbon means 12 g. Therefore amount of carbon dioxide is 12 + 16 = 28. Am I correct?

From the equation, $$\ce{C + O2 -> CO2},$$ we can see that one mole of $$\ce{C}$$ reacts with one mole of $$\ce{O2}$$.

Therefore, let us calculate the amount of each reactant present.

The amount of $$\ce{C}$$ is already given: $$n(\ce{C}) = \pu{1 mol}$$.

The molar mass of $$\ce{O2}$$ is $$M(\ce{O2}) = \pu{32 g//mol}$$, so $$\pu{16 g}$$ of $$\ce{O2}$$ are $$\pu{0.5 mol}$$.

Since one mole of $$\ce{C}$$ only reacts with one mole of $$\ce{O2}$$, there remain $$\pu{0.5 mol}$$ of unreacted $$\ce{C}$$, while $$\pu{0.5 mol}$$ of $$\ce{C}$$ react with $$\pu{0.5 mol}$$ of $$\ce{O2}$$.

In formal terms, oxygen is called the limiting reactant as it limits the amount of product formed.

From the equation, one mole of $$\ce{CO2}$$ is produced per each mole of $$\ce{C}$$. Therefore, $$\pu{0.5 mol}$$ of $$\ce{CO2}$$ is produced.

• The name of the quantity $n$, which is usually expressed in the SI unit mol, is “amount of substance”. It shall not be called “number of moles”, just as the quantity “mass” shall not be called “number of kilograms”. According to SI, ISO, and IUPAC, the words “of substance” can be replaced to specify the substance, so that one may talk of “amount of carbon dioxide”. Although the word “amount” has a more general dictionary definition, this abbreviation may be used for brevity. Therefore, “amount of carbon dioxide” is the amount of substance $n(\ce{CO2})$, which is usually expressed in mol. – Loong Sep 6 '16 at 19:34
• @Loong Wow. My school teaches me "number of moles". – DHMO Sep 6 '16 at 19:37
• Yes, the name “number of moles” is often used for “amount of substance”, but this is deprecated. – Loong Sep 6 '16 at 19:40
• Oh ok.Since 1 mole of oxygen required for producing 1 mole carbon dioxide.16g of oxygen=0.5 moles of oxygen are there.So,0.5 moles of carbon dioxide is required,right? – Abhijith Dileep Kumar Sep 7 '16 at 10:51
• @Abhijith It would be more accurate to say that only 0.5 moles of carbon dioxide reacted. – DHMO Sep 7 '16 at 10:55

The one mole of carbon would react with one mole of dioxygen to give one mole of carbon dioxide.

$$\pu{12 g}$$ of carbon would therefore react with $$\pu{32 g}$$ of $$\ce{O2}$$ to give $$\ce{44 g}$$ of $$\ce{CO2}$$.

As someone else has pointed out, it would be tricky to get absolutely all the carbon to burn in oxygen unless you set it up in a particular way to do so. Probably in real life some would not burn efficiently and you might end up with carbon monoxide, which is poisonous if you breath it in. Some carbon might also stay as carbon (soot).

• Did you read in the question that the available amount of dioxygen is limited? – Arsak Sep 7 '16 at 6:34