Chemical reactions involves the rearrangement of atoms to beget new chemicals. Often these reactions are captured succinctly in what is called a chemical equation. For example, if we want to show how carbon reacts with oxygen to make carbon dioxide we would write the follow chemical equation.

The plus sign means “reacts with” and the arrow means “to make”. Therefore, we can write this chemical equation in English by saying

Carbon reacts with oxygen to make carbon dioxide

Chemical equations need to balance. If you look at the example above, there are the same number of atoms for each element on each side. The example above is rather simple, however, sometimes it is a little trickeier to tell if an chemical equation is balanced.

In the reaction above we have to look carefully to see if the chemical equation is balanced. Starting on the left we have 1 carbon and 4 hydrogens. Next, there is a 2 which means that we multipl everything by 2 that is next to it. In other words, we do not have 2 oxygen atoms but rather 4 (2 x 2 = 4). After the arrow, we have 1 carbon and 2 oxygen atoms and after the plus sign we have 4 hydrogen atoms (2 x 2 = 4) and 2 oxygen (2 x 1 = 2). If we line everything up you can see that this equation is balanced.

	Left Side	Right Side
C	1 x 1 = 1	1 x 1 = 1
H	4 x 1 = 4	2 x 2 = 4
O	2 x 2 = 4	2 + (2 x 1) = 4

There are times when you need to balance a chemical equation. This can get really challlenging but we will do a simple example below.

The chemical equation above is not balance as you can see below

	Left Side	Right Side
H	1 x 2 = 2	1 x 1 = 1
Cl	1 x 2 = 2	1 x 1 = 1

The table above is one process in balancing an equation. We need both sides to equal each other and the simplest way to do this is to multiple the right side by two and we get the following table.

	Left Side	Right Side
H	1 x 2 = 2	2 x 1 = 2
Cl	1 x 2 = 2	2 x 1 = 2

Below is what our balanced chemical equation looks like.

As mentioned previous, placing the 2 in front of the molecule means multiply everything by 2. Such an example like this is really simple but provides a basic understanding of this process.

Conclusion

Chemical equations can be really fun to deal with once you understand how this works. In the beginning, it can be truly frustrating but perseverance will make the difference.

In this post, we will focus most of our attention on physical changes in chemistry with a brief look at chemical changes.

Changes

Physical change is a change to a substance that does not alter the chemical composition. For example, boiling water is a physical change. Generally, physical changes are easy to reverse, such as when steam is cooled to become liquid water.

Chemical change is a change that alters the chemical composition of a substance. An example would be various forms of cooking, such as frying potatoes to make french fries. Unlike physical changes, chemical changes are much harder to reverse. Just as it is impossible to turn french fries back into raw potatoes.

A specific type of physical change is called phase change. There are several different types of phase changes, as listed below.

• melting
• vaporizing
• freezing
• condensing
• sublimation

Many of these are obvious, but they will be explained for clarity. Melting involves a substance moving from a solid to a liquid. Vaporizing takes place as a substance moves from liquid to gas. A substance that moves from a gas to a liquid is called condensing. Freezing is the process of a liquid becoming a solid. Sublimation is a solid moving straight to a gas.

The first four-phase changes are commonly seen in water. Ice melts to become liquid water, water boils/evaporates (vaporizes) to become steam. Water freezes to become ice; in the early morning, it is common in many places to see water on plants due to condensation. Sublimation is tricker to see on a day-to-day basis. The most common example involves carbon dioxide, aka dry ice, which is a favorite tool for Halloween. Other substances that sublimate include arsenic, iodine, and naphthalene (used for mothballs).

Phase changes are related to the kinetic theory of matter, which we will now turn our attention to.

Kinetic Theory of Matter

The kinetic theory of matter states that Molceults have space between them and are in constant random motion. We can say that the more heat, the faster the motion because more energy is present. For solid, the molecules can vibrate, but that is essentially it. All solids are vibrating, such as tables, chairs, desks, etc. However, the vibration is random, and thus the vibrations cancel each other.

Liquids can clearly move about, and this is why they cannot keep a single shape but is formed by their circumstances. This also applies to gasses. The real difference between the various phases is the space around molecules and the speed at which they are moving. When energy is added, molecules move apart and move faster. This explains a solid becoming a liquid and a liquid a gas.

Water breaks many rules in relation to the Kinetic theory of matter. When water freezes, instead of the molecules getting closer together, they actually push out and are thus less dense than water. This is one reason why ice floats and why you would find frozen ice on the top of a lake. The ice floats to the top, and by being on top, it insulates the animals inside the lake from the cold above.

Conclusion

Physical changes play a major role in all of our lives. The phase changes of water are used for various purposes in everyday life. It is beneficial to understand these concepts as they are so commonly encountered.

Matter is the physical stuff that everything around us is generally made of. Trees, birds, water, etc., are all examples of matter. Since almost everything is considered matter, scientists have naturally found ways to classify matter to better understand it.

Types of Matter

One way matter is classified whether it is a pure substance or a mixture. A pure substance is a substance that has the same properties throughout out it. An example of a pure substance would be salt or sugar. Both of the substances are only made of salt or sugar, and the properties of these two substances are the same if you have one or the other in a sample.

On the other hand, a mixture is a combination of two or more substances. For example, if you have salt and pepper inside the same shaker, this is a mixture. This is because separating the salt and the pepper from each other is possible. Separating pure substances is generally not possible physically. However, pure substances can further be broken down into elements and compounds.

Elements are fundamental substances that cannot be broken down into simpler substances. The periodic table contains all known elements. Examples include oxygen, sodium, carbon, etc. Compounds are pure substances that are made of two or more elements. Compound examples include salt, sugar, carbon dioxide, etc.

More on Mixtures

Returning to mixtures, there are two types of mixtures: homogenous and heterogeneous. Homogenous mixtures have the same composition throughout the sample. Examples include milk and sugar water. In both of these examples, the substances that make up the mixture are evenly spread throughout the sample.

Heterogeneous mixtures have different compositions in parts of the sample. A classic example of this is salad dressing. When salad dressing is allowed to sit, it separates clearly into the various substances/homogenous mixture that it is made up of. This is why salad dressing must be shaken before it is enjoyed.

Law of mass conservation

Antoine Lauren de Lavoisier developed the law of mass conservation, which states that in any chemical or physical process, the total mass of everything involved must remain the same. This means that if you start with 5 kg of wood and burn it, there will still be 5kg of matter in a different form. You might see a pile of ashes that weighs less but what happens is that some of the matter was converted to gases and smoke in the burning process. Essentially, matter can be created or destroyed but can only be converted or broken down.

Conclusion

No pun intended, but matter matters. For students, it is important to develop an understanding of concepts related to chemistry. Doing so may help at least some of them prepare for whatever occupation they may have in the future.