In chemistry, a word equation is a chemical reaction expressed in words rather than chemical formulas. A word equation should state the reactants (starting materials), products (ending materials), and direction of the reaction in a form that could be used to write a chemical equation.
There are some key words to watch for when reading or writing a word equation. The words "and" or "plus" mean one chemical and another are both reactants or products. The phrase "is reacted with" indicates the chemicals are reactants. If you say "forms", "makes", or "yields", it means the following substances are products.
When you write a chemical equation from a word equation, the reactants always go on the lefthand side of the equation, while the reactants are on the righthand side. This is true even if the products are listed before the reactants in the word equation.
Key Takeaways: Word Equations
- A word equation is an expression of a chemical reaction or mathematical equation using words rather than letters, numbers, and operators.
- In chemistry, a word equation indicates the order of events of a chemical reaction. The number of moles and types of reactants yield the number of moles and types of products.
- Word equations help in learning chemistry because they reinforce the thought process involved in writing a chemical reaction or equation.
Word Equation Examples
The chemical reaction 2 H2(g) + O2(g) → 2 H2O(g) would be expressed as:
hydrogen gas + oxygen gas → steam
As a word equation or as "Hydrogen and oxygen react to form water" or "Water is made by reacting hydrogen and oxygen."
While a word equation doesn't ordinarily include numbers or symbols (Example: You wouldn't say "Two H two and one O two makes two H two O", sometimes it is necessary to use a number to indicate the oxidation state of a reactant so that a person writing a chemical equation can do it correctly. This is mostly for the transition metals, which can have multiple oxidation states.
For example, in the reaction between copper and oxygen to form copper oxide, the chemical formula of copper oxide and the number of copper and oxygen atoms involved depends on whether copper(I) or copper(II) participates in the reaction. In this case, it would be fine to say:
copper + oxygen → copper(II) oxide
Copper reacts with oxygen to produce copper two oxide.
The (unbalanced) chemical equation for the reaction would start out as:
Cu + O2 → CuO
Balancing the the equation yields:
2Cu + O2 → 2CuO
You would get a different equation and product formula using copper(I):
Cu + O2 → Cu2O
4Cu + O2 → 2Cu2O
More examples of word reactions include:
- Chlorine gas reacts with methane and carbon tetrachloride to produce hydrogen chloride.
- Adding sodium oxide to water produces sodium hydroxide.
- Iodine crystals and chlorine gas react to make solid iron and carbon dioxide gas.
- Zinc and lead two nitrate make zinc nitrate and lead metal.
which means: Zn + Pb (NO3)2 → Zn(NO3)2 + Pb
Why Use Word Equations?
When you're learning general chemistry, work equations are used to help introduce the concepts of reactants, products, the direction of reactions, and to help you understand precision of language. They may seem annoying, but are a good introduction to the thought processes required for chemistry courses. In any chemical reaction, you need to be able to identify the chemical species that react with each other and what they make.
Word Equations in Other Sciences
Chemistry isn't the only science to use equations. Physics equations and mathematical equations may also be expressed in words. Usually in these equations two statements are set to be equal to each other. For example, if you way "force equals mass multiplied by acceleration" then you are providing the word equation for the formula F = m*a. Other times, one side of the equation may be less than (), less than or equal to, or greater than or equal to the other side of the equation. Addition, subtraction, multiplication, division, logs, square roots, integrals, and other operations can be stated in word equations. However, complex equations that contain parentheses to describe the order of operations are very hard to understand as word equations.
- Brady, James E.; Senese, Frederick; Jespersen, Neil D. (December 14, 2007). Chemistry: Matter and Its Changes. John Wiley & Sons. ISBN 9780470120941.