September 13th - Nothing But Balancing!

Today we learned all about word equations and balancing chemical equations.

We started class today with a review of the homework questions about lab safety. These questions reviewed:

• the basic safety rules to be followed in a laboratory (such as following the directions of the teacher and disposing of chemicals properly)
• the importance of tying back hair and rolling up sleeves (so that they do not droop into an open flame or come into contact with chemicals)
• examples of how basic chemistry safety can also be applied to other aspects of life, such as changing a tire or baking (for example, it is important to follow directions while changing a tire or baking so that you do not get into an accident or cut yourself in the kitchen)

 As you can see in the photo above, nobody is too cool to practice safe behaviour in the lab.

Shortly after going over the questions, we learned all about word equations and balancing chemical equations. For example, you may be reading your textbook when you encounter a sentence such as this:

Methane gas reacts with oxygen gas to produce carbon dioxide gas and water.

This is known as a word equation, the simplest form of an equation. It gives us the names of the reactants (the chemicals that react together) and the product(s) (the chemicals that are produced). It could also be written as:

methane + oxygen --> carbon dioxide + water

We learned that chemical reactions can also be represented by sentences known as chemical equations (or formula equations). Here's an example of a chemical equation:

CH₄ + O₂ --> CO₂ + H₂O

The letters that you see represent the atoms, molecules or compounds in the reaction. For example, on the left side of the equation, you can see that both methane and oxygen are present. You will also notice a plus sign (+) and an arrow ( --> ). The plus sign means 'reacts with', and the arrow means 'to produce'. The direction that the arrow is pointing indicates the direction of the reaction. The subscripts indicate the number of each element in the molecule, atom, or compound. If a molecule or compound is in brackets with a subscript on the outside, then the subscript applies to every element in the brackets. A chemical equation can be read the same way as the word equation.

It is also important to understand the products in the reaction. This is a combustion reaction, where a fuel reacts with oxygen to produce carbon dioxide and water. In this specific equation, the atoms of carbon and hydrogen break apart and end up in different products. The old bonds break apart and are replaced with new bonds, resulting in completely new molecules. However, you may be wondering why there are fewer atoms of hydrogen in the products than in the reactants. This, my friends, is where the law of conservation of matter comes into play. This law states that all matter has mass, which cannot be created or destroyed in a chemical reaction. In other words, those hydrogen atoms have to go somewhere. But where? To solve this problem, we need to perform the next step, called balancing.

The law of conservation of mass tells us that there has to be an equal number of specific atoms on both sides of the equation. When this law is observed, it is considered balanced. We begin by counting the number of atoms on each side of the equation. Here is the chemical formula from above:

CH₄ + O₂  --> CO₂ + H₂O

This tells us:

That we have one carbon atom (reactant).

That we have four hydrogen atoms (reactants).

That we have two oxygen atoms (reactants).

That we have one carbon atom (product).

That we have two hydrogen atoms (products).

That we have three oxygen atoms (products).

This equation is unbalanced, so we must use coefficients to balance it. For example, we multiply 
the number of hydrogen atoms by 2 on the right side to make the numbers even. This way, we 
can follow the law of conservation of matter. If you do it correctly, it should end up looking like this:

CH₄ + 2 O₂  --> CO₂ + 2 H₂O

Here is an awesome video of the reaction you have just balanced:

This skill is very important, as it will allow us to better understand the rest of the curriculum.

But we're not done yet! One of the important, but subtle, parts of balancing equations is the inclusion of the phase symbol. Phase symbols are subscripts that indicate the state of matter of the chemical. The four states of matter that we study in Chemistry 11 are solids (s), liquids (l), gases (g), and aqueous (aq) solutions (dissolved in water). To complete the chemical equation, we must add the phase symbols:

CH₄ (g) + 2 O₂ (g) --> CO₂ (g) + 2 H₂O (l)

In the above reaction, none of the reactants or products are solutions. In chemistry, a solution is something dissolved in water (the aqueous state). It is important that chemical and word equations indicate the state of matter in the form of phase symbols or words.

But wait, there's more! Here's something fun to keep you interested:

We also learned about diatomic and polyatomic molecules. Diatomic ('di' meaning two, and 'atomic' referring to an atom) molecules are molecules that exist in pairs of two. The diatomic molecules are:

H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂

_{Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, and Iodine}

Polyatomic molecules also have more than one of the same element attached together. The important ones to know for Chemistry 11 are:

P_4, S₈

Tetraphosphorus, Octasulfur

Be careful, though! It is often easy to forget about these exceptions when writing or balancing equations!

Posted by Michael.