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Course: High school chemistry > Unit 3
Lesson 1: Representing chemical reactionsSymbols in chemical equations
Learn the meaning behind the symbols we use to represent chemical reactions.
Symbols in chemical equations
Chemistry is a universal language used by people around the world. So, we as scientists can communicate with each other about chemistry even if we speak different languages in our day-to-day lives! All we have to do is follow consistent rules when talking about certain scientific concepts.
For example, we can describe the chemical reactions that occur in the physical world using chemical equations. These equations include symbols with specific meanings. The key features of a chemical equation are pointed out here:
- Reactants are the substances we start with. They are written on the left side of the arrow.
- Products are the substances that are created. They are written on the right side of the arrow.
- The arrow indicates that a chemical change has occurred.
- Coefficients are the larger-sized numbers that come before a chemical formula. They indicate how many separate instances of substance are present in the reaction. In the example above, two separate silver atoms
- Subscripts are the smaller-sized numbers that come after an element symbol. These indicate there are multiple instances of the same element within a substance. In the example above, two silver atoms
- States of matter are the one or two-letter abbreviations that come after each substance in a chemical equation. These indicate what physical form the substance takes in the chemical reaction described.
| Symbol | Meaning |
|---|---|
| solid | |
| liquid | |
| gas | |
| aqueous* |
*the substance is dissolved in water
Counting atoms using subscripts and coefficients
It is often important to know how many atoms of each element are being shown in an equation. We can use the subscripts and coefficients in the equation to figure this out.
Let’s look at some examples:
Example 1:
How many oxygen atoms are represented in the formula
- 3 oxygen atoms
Example 2:
How many oxygen atoms are represented in the formula
- 6 oxygen atoms
Example 3:
How many oxygen atoms are represented by
- 18 oxygen atoms
Try it: Counting atoms
Want to join the conversation?
in question 2 and 3, why is there a compound but it say 2 of it like 2FE3(PO4)2 instead of 2FE3P2O8(5 votes)
The reason why it's written as 2Fe3(PO4)2 and not 2Fe3P2O2 is because the parentheses around the PO4 show that PO4 is a group of atoms, and the 2 at the back shows that there are 2 groups of PO4.(12 votes)
why do we also multiply the coefficient why cant we add it?(2 votes)
You must multiply the coefficient as it represents how many of a certain compound there is. For example, CO(2) - as a single compound - has one carbon, and two oxygen. 2CO(2) means that there is two CO(2) compounds, and when you count the atoms in total you must distribute the coefficient (the two) to the rest of the subscripts.
In total, there would be 2 carbon atoms, and 4 oxygen atoms. Hope this helped!(1 vote)
To find the number of oxygen atoms, why is it necessary that we multiply when there is a number of moles in front of an element's symbol?(2 votes)- Do we multiply by the first number always?(2 votes)
yes, if there is one.(1 vote)
- Does the first number apply to all atoms in the problem?(2 votes)
- Take Hydroxide; OH. If you put a 2 in front of it (2OH) then you have 2 Oxygen and Hydrogen atoms. So yes. Although, if you take Oxygen and Hydrogen separately and then put a 2 in front (2O H), then no.(1 vote)
why is the first number significant in the problems?(1 vote)- That would be the coefficient. It is used to represent how much of a compound there is in a formula. When counting atoms, you must distribute the compound and multiply it by the subscripts.(1 vote)
- Do the coefficient have to be added or multiplied with the subscripts?(1 vote)
- Multiplied! The coefficient represents the amount of a compound there is in your formula.(1 vote)
- Why do we have to multiply the first number by the last.(1 vote)
- This is because of the coefficient. When you count atoms, you must multiply the coefficient times the amount of subscripts in your entire compound.(1 vote)
