balancing chemical equations

Word Equations

A thorough knowledge of chemical equations is required to understand how chemical reactions take place. Chemical equations are a shorthand way of describing the composition and amounts of all reactants and products in the reaction. Consider your face a product made up of reactants (or organs) such as a pair of eyes, ears, lips, and a nose. So, if you were able to describe your face using a word equation, it would look something like this: eye + nose + ears + lips → face (reactants) (product) A word equation is an accurate statement but it has a few drawbacks. First, it's not a universal statement. A French chemist would not necessarily understand the meaning of these English terms. Second, a word equation is a qualitative statement, not a quantitative one. It tells us in broad terms which reactants are involved, but it does not tell us how much of each substance. To overcome the first drawback, scientists created symbols for each of the elements, such as H for hydrogen and O for oxygen. They also developed a system of nomenclature that allows each substance to be represented by a formula. So, the word water might not make sense to a French scientist, but the molecular formula, H2O, would be instantly recognizable. To overcome the second drawback, scientists figured out a way to balance equations so that the equation represents the precise number of reactants involved

Balancing Chemical Equations

Balancing an equation is important because it gives you information about the exact number of reactants required to make the product. For example, with the "face equation" we know that a face is formed only when two eyes, two ears, two lips, and one nose are available. You can't make a proportioned face with one eye or two noses. To get the desired product, you need to mix the reactants in a certain ratio. A balanced chemical equation takes care of that ratio. Before you learn how to balance chemical equations, remember that a properly balanced chemical equation should follow the law of conservation of mass. Therefore, each side of the equation must contain the same number of atoms of each element. Now, let's start the balancing act! The first step in balancing a chemical equation is to ensure that the chemical formulas of the reactants and products are correct. Let's consider the formation of water molecules. Using the correct formulas for molecular hydrogen, molecular oxygen, and water, we can form the following skeleton equation: H2 + O2 → H2O A quick look at this equation will show you that it is not balanced. This is because while there are two atoms of hydrogen on both sides of the equation, there are two atoms of oxygen on the left side and only one atom on the right. This means that one atom of oxygen is unaccounted for. Since matter is always conserved, this is an unacceptable situation. One tempting way to balance the equation H2 + O2 → H2O is to remove the subscript from the oxygen molecule. But changing a subscript in a chemical formula changes the actual identity of the substance. For example, removing one oxygen atom from a carbon dioxide molecule turns it into the highly toxic carbon monoxide molecule. Similarly, molecular oxygen consists of two atoms of oxygen, not one. Instead of changing the subscript, how about multiplying the amount of products or reactants? This is acceptable since it only changes the amounts of the substances, not their identities. In the equation above, we need two atoms of oxygen on the right to balance the two atoms of oxygen on the left. We can do that by doubling the number of water molecules, as shown in the equation below. So the coefficient 2 is placed in front of H2O, making it 2H2O. A whole number coefficient in front of a chemical formula tells how many units of that substance are needed for the reaction. H2 + O2 → 2H2O Now, we have two molecules of water on the right, totalling two atoms of oxygen and four atom of hydrogen. But on the left, there's only two atoms of each. The oxygen atoms are balanced, but not the hydrogen atoms. Let's handle them next. We can summarize the process of balancing an equation into the following steps: Write an unbalanced equation using the correct chemical formulas. Balance each element one at a time by inserting appropriate coefficients. If a coefficient is absent, it is assumed to be 1. Do not change the subscripts of the formula. Check whether the number of atoms of each element is equal on both sides of the equation. Reduce all the coefficients of the equation to their lowest possible ratio. You can use the Equation Balancer tool to balance a chemical equation. In the tool, analyze the equation and enter the appropriate coefficients in the boxes provided to balance the equation. If the reactant or product does not require a coefficient, enter a 1 in the box. Now balance the following chemical equation yourself. Click the link below to load the equation in the Equation Balancer tool. Cu + S → Cu2S (Note: This equation is unbalanced as written.)

Chemical Equations

A chemical reaction occurs when one or more substances combine or decompose to form a new substance that has entirely different chemical and physical properties. For example, when you bake a cake, you use butter, flour, sugar, and eggs. These ingredients each have different chemical and physical properties. However, they undergo chemical changes that turn them into a cake when they are baked together. Similarly, when a car rusts in the presence of moisture, iron and oxygen combine and form iron(III) oxide. In a chemical reaction, the substances present at the start of the reaction are called reactants, and the substances that are newly formed are called products. In the case of the rusting car, the reactants are iron and oxygen and the product is iron(III) oxide—the rust. Another common example of a chemical reaction is the combination of hydrogen gas and oxygen gas to form water. In this case, hydrogen and oxygen are the reactants and water is the product.

Reversible Reactions

Chemical reactions do not always convert reactants completely into products. Many chemical reactions are reversible, which means that the reactants react to form products and the products simultaneously break up to form the reactants. In other words, reversible reactions proceed in both the forward and reverse directions simultaneously. One example of a reversible reaction is the reaction of nitrogen gas and hydrogen gas to form ammonia gas. The chemical equation is shown above. The forward reaction is read from left to right, where nitrogen gas reacts with hydrogen gas to form ammonia. The reverse reaction is read from right to left to show that ammonia breaks up into hydrogen gas and nitrogen gas. Instead of writing two equations, a double arrow is used to indicate that both reactions are happening at the same time. A reversible reaction contains two reactions that occur simultaneously in opposite directions and therefore has the potential to achieve chemical equilibrium.

Chemical Equations

Let's go back to our word equation and apply what we just learned. Now, instead of using words in our "face equation" that may only be understood by those who speak the language, we can use symbols. For example, Ey will represent an eye, N for nose, Er for an ear, and L for a lip. These symbols can be universally understood by everyone. Using these symbols, this is how the equation would look: Ey + N + Er + L → EyNErL (reactants) (product) But we know that a face has to have two eyes, two ears, two lips, and one nose. So, the equation of a face that represents the correct number of reactants and product would be expressed as: 2Ey + N + 2Er + 2L → Ey2NEr2L2 (reactants) (product) The above equation is now balanced. This means that the number of ingredients in the reactants is equal to the number of ingredients in the product. In other words, it follows the law of conservation of mass. Let's learn more about this law.

Law of Conservation of Mass

The law of conservation of mass states that matter can neither be created nor destroyed. So, the products formed in a reaction must have the same total mass as that of the reactants present before the reaction took place. On the other hand, atomic theory—the study of matter—says that atoms maintain their identities in a chemical reaction. These statements taken together mean that any equation for a reaction must be balanced. There must be as many atoms of each element on the products side as there are on the reactants side. You will learn how to balance equations later in this lesson. First, let's explore the components of an equation.

The four steps to balance a chemical equation are

Write an unbalanced skeleton equation using the correct chemical formulas. Balance each element in the equation one at a time by inserting appropriate coefficients. If a coefficient is absent, it is assumed to be 1. Do not change the subscripts of the formula. Check whether the number of atoms of each element is equal on both sides of the equation. Reduce all the coefficients of the equation to their lowest possible ratio.