If you are new to chemistry, you might have encountered the terms “law of conservation of mass” and “balancing equations” in your studies. But what do they mean and how are they related? In this article, we will explain these concepts in a simple and easy way, using examples and illustrations.
Contents
What is the Law of Conservation of Mass?
The law of conservation of mass states that the total mass of a system remains constant during any physical or chemical change. This means that the mass of the reactants (the starting materials) is equal to the mass of the products (the final materials) in any process. No matter how the atoms are rearranged or transformed, their total mass does not change.
The law of conservation of mass was first discovered by Antoine Lavoisier, a French chemist, in the late 18th century. He performed many experiments to show that the mass of a substance does not change when it undergoes a chemical reaction. For example, he burned a piece of wood in a closed container and measured the mass of the container before and after the reaction. He found that the mass was the same, even though the wood was turned into ash, carbon dioxide, and water vapor.
What is Balancing Equations?
Balancing equations is a method of writing chemical equations that shows the same number of atoms of each element on both sides of the equation. This is important because a chemical equation must obey the law of conservation of mass and the law of constant proportions, i.e. the same kind and amount of matter exists before and after the reaction.
A chemical equation is a symbolic representation of a chemical reaction, using chemical formulas and symbols. For example, the equation for the combustion of propane (a gas used for cooking and heating) with oxygen is:
C3H8 + O2 → CO2 + H2O
This equation tells us that one molecule of propane reacts with oxygen to produce one molecule of carbon dioxide and one molecule of water. However, this equation is not balanced, because it does not show the same number of atoms on both sides. To balance this equation, we need to add coefficients (numbers) in front of the formulas to indicate how many molecules or moles of each substance are involved in the reaction. A balanced equation for this reaction is:
C3H8 + 5O2 → 3CO2 + 4H2O
This equation shows that one mole of propane reacts with five moles of oxygen to produce three moles of carbon dioxide and four moles of water. Now, we can see that there are 3 carbon atoms, 8 hydrogen atoms, and 20 oxygen atoms on both sides of the equation, satisfying the law of conservation of mass.
How to Balance Equations?
There are different methods to balance equations, but one common way is to use the following steps:
- Identify the reactants and products and write their formulas.
- Count the number of atoms of each element on both sides of the equation.
- Start with an element that appears only once on each side and adjust its coefficient until the number of atoms is equal on both sides.
- Repeat step 3 for other elements until all elements are balanced.
- Check your work by counting the atoms again.
Let’s try an example: Balance the equation for the reaction between iron (Fe) and sulfur (S) to form iron sulfide (FeS).
Step 1: The reactants are iron and sulfur and the product is iron sulfide. Their formulas are Fe, S, and FeS.
Step 2: The number of atoms on each side is:
| Element | Reactants | Products |
| Fe | 1 | 1 |
| S | 1 | 1 |
Step 3: The element Fe appears only once on each side, so we do not need to change its coefficient. The element S also appears only once on each side, but its coefficient is already equal to 1, so we do not need to change it either.
Step 4: There are no other elements to balance, so we are done.
Step 5: The final balanced equation is:
Fe + S → FeS
We can check that there is one atom of Fe and one atom of S on both sides.
Why is Balancing Equations Important?
Balancing equations is important because it helps us understand how chemical reactions work and how much reactants and products are involved in a reaction. By balancing equations, we can:
- Predict how much product will be formed from a given amount of reactants or vice versa.
- Calculate how much energy is released or absorbed by a reaction.
- Compare different reactions based on their efficiency or yield.
- Design experiments or industrial processes based on stoichiometry (the quantitative relationship between reactants and products).
Balancing equations is also a skill that is required in many chemistry courses and exams, so it is essential to master it if you want to succeed in chemistry.
Summary
The law of conservation of mass states that the mass of a system does not change during any physical or chemical change. Balancing equations is a method of writing chemical equations that shows the same number of atoms of each element on both sides of the equation. Balancing equations is important because it helps us understand and calculate various aspects of chemical reactions. To balance equations, we need to identify the reactants and products, count the atoms, adjust the coefficients, and check our work.
