8 Basic Laws of Chemistry – Theories – Principles

Basic laws of chemistry are the law that is widely applied or used in chemistry science. Chemistry is a branch of science that study chemical property, elements, molecules, and many other things in our life. Because the scope of chemistry science is wide, people tend to back-off from learning chemistry, even only for a little bit of it. We believe that having some basic understanding of our world is important, and we can do it, like it or not, by understanding the basic laws of chemistry science that are widely beneficial in fact only if we apply it to our daily activities. After reading this article, you should be able to explain to your little sister, why your computer get hot after we play games for an entire day.

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1. Lavoisier’s Law

Lavoisier’s law is one of the fundamental laws of chemistry. As you might guess, Antoine-Laurent de Lavoisier or Lavoisier is the man who discovered and theorised this law. Basically, this law tells us that in a closed systems, the mass before and after reaction of the chemical compound is the same. That’s why we also call this theory as a theory or law of conservation of mass.

Mathematical formulas

There is no definite formula of Lavoisier’s law around. But, in its simplest sense, we can describe it using a formula like this:

m1 = m2;

Where m1 stands for the sum of mass before reaction and m2 stand for the sum of mass after the reaction. Remember that m1 or m2 does not necessarily reflect one compound, it can also reflect the sum of mass from two or more compound in the reaction.

Example of application

We can use Lavoisier’s law to explain why the sum of mass in a closed systems after a reaction does not change.

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2. Dalton’s law of multiple proportions

John Dalton is a British chemist who discovered a lot of things in chemistry. One of them is the law of multiple proportions that is quite useful in stoichiometry. He published it in the first part of the first volume of his “New System of Chemical Philosophy” (1808). This law works well with simple compound, but it will be harder to notice at a larger compound and even fails to apply with non-stoichiometric compounds and also doesn’t work well with polymers and oligomers.

Dalton’s law of multiple proportions says that: If there are two elements that can form more than one compound, then the ratios of the masses of the second element which is combined with a fixed mass of the first element will be ratios of small whole numbers.

Mathematical formulas

There is no definite formula reflecting Dalton’s law of multiple proportions.

Example of application

To demonstrate this law, let’s say we have a molecule of carbon and oxygen. We will use it to create an oxide.We know that carbon and oxygen can form CO and CO2 respectively. After calculating their mass, scientist found that the ratio of the mass of oxygen between the first CO and CO2 is 1:2. This also means that we can calculate if there are say, 800 grammes of oxygen in a compound of CO, then for CO2, it will contain at least 1600 grammes.

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3. Dalton’s law of partial pressure

Another basic law in chemistry founded by Dalton is Dalton’s Law of Partial Pressures. In brief, this law states that the sum of the partial pressures of the gases in the mixture of the system is equal to the total pressure exerted by a mixture of gases. A gaseous compound will diffuse in a container to fill up space it is in. They will only interact with their own kind of gases, therefore there won’t be any reaction between a different gaseous compound.

In an ideal gas system, the pressure inside the system is dependent to its collisions with the container. A gas compound will expand itself to fill the container it is in without affecting the pressure of another gas. However, that the pressure of a certain gas is based on the number of moles of that gas, the volume and temperature of the system. Therefore, the pressure of the gas will be dependent on the how many molecules of that gas inside the system, the volume, and also temperature. Because the gases in a mixture of gases compound are in one container, the Volume (V) and Temperature (T) for the different gases are the same as well. Each gas also exerts its own pressure, that can be added up to find the total pressure of the mixture of gases in the system.

Mathematical formula

Dalton’s law of partial pressure formula looks like this:

Ptotal = P1 + P2 + P3….

Because of that pressure relationship, we can also derive it to a formula below (which is probably more familiar to some of us)


We can use this equation to find the total number of moles in systems. This can be done by converting grammes to moles and using Dalton’s law to find the pressure.

Example of application

The application of the law of partial pressure can be seen when we try to calculate the pressure inside a closed system of gas and water.

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4. Proust’s Law of Constant Proportion

Proust’s law of constant proportion is also known as the law of definite proportions. This law, just like the law of multiple proportions from Dalton, is rooted in Lavoisier’s law of mass conservation. However, they are not the same, of course. Joseph Proust, who is a chemist from French, states in this law, that:

“A chemical compound will always contain the same elements combined together in the same proportion by mass.”

Mathematical formulas

There is no definite formula of this law. But, we can simply describe it as a comparative formula of elements and its mass. For example Xn1Yn2, where X and Y stand for the name element in a compound, and n stands for it the number of its elements within the formula. If the number of n (for each of the element inside the compound) get larger, the sum of mass will also get larger.

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5. Gay-Lussac’s Law

Gay-Lussac’s Law of Gas Pressure and Temperature Relationship. Between 1800 and 1802, Gay-Lussac discovered the relationship between the pressure and temperature of a fixed mass of gas’ kept at a constant volume. He discovered this while building an “air thermometer”.

Gay-Lussac’s law of pressure and gas temperature relationship states that the pressure of a gas in a system is proportional to its temperature, only and if only the mass and the volumes are constant. It means that if the pressure increase, the temperature will also get increased, and vice versa.

Mathematical formula

We can define Gay-Lussac’s law of pressure and temperature relationship mathematically like this (in the case of comparison before and after a change in a system occurs):

P1 / T1 = P2 / T2


P is the pressure of the gas,
T is the temperature of the gas (measured in kelvins),
This law is true at least because of two reasons. First, a temperature is a measure of the average kinetic energy of a substance. Second, as the kinetic energy of gas increases, its particles will collide with the container walls more rapidly, and so increasing the pressure within the system.

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6. Avogadro’s law

Avogadro’s law is one of the basic law in chemistry. Amedeo Avogadro found it around 1811. Basically, Avogadro say in this law that a different gas will have the same amount of molecules if their volumes, temperature, and pressure are identical. In an ideal gas, for a given mass of it, the volume and moles of the gas are proportional as long as the temperature and pressure are kept constant. In most of the cases, this law only functions as an approximation, because the number of molecules is frequently different from what the law has stated to some degree. But still, this law is quite useful for the scientist.

Mathematical formula

We can express Avogadro’s law like this:



V is the volume of the gas
n is the amount of substance of the gas (in moles).
k is a constant equal to RT/P, where R is the universal gas constant, T is the Kelvin temperature, and P is the pressure. As long as temperature and pressure are constant, RT/P can be represented as k. To compare the same substance under two different sets of conditions, we have this formula:

V1 / n1 = V2 / n2

This equation shows us that as moles of gas increases, the volume of the gas also increases.

Example of application

Based on this law, scientist (or us, in a broader sense) has found a way to determine the molar volume of a gas (of any kind) at a standard temperature and pressure. Right now, the molar volume of a gas at STP (standard temperature and pressure) is 22.4 litres.

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7. Boyle’s law

Boyle’s law is an experimental gas law that proposes an inverse relationship between pressure and volume of a gas. This law explains how a gas pressure will increase if the volume of the container decrease. He also said that the pressure given by a mass of an ideal gas is going to be inversely proportional to the volume where it occupies. But, only if the amount of gas and its temperature stay the same in the closed system.

Mathematical formula

Mathematically, Boyle’s law looks like this:


where P is the pressure of the gas, V is the volume of the gas, and k is a constant value representative of the temperature and volume of the system. To compare the same substance under two different sets of the condition, we can express it like this:


This equation shows us that as the volume of the gas increases, the pressure inversely decreases in proportion. Similarly, as volume decreases, the pressure of the gas increases. You can see that, when the temperature is constant, the amount of energy in the system will still be the same. And that’s why k will stay constant.

Example of application

We can explain how our respiratory system work using Boyle’s law. As we inhale or exhale, it will create changes in our lung volumes. This will result in different of pressure between the air inside our lungs and the environment. That different will, in turn, precipitates exhalation or inhalation as air moves from high to lower pressure.

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8. Charles’s Law of Volumes

In chemistry, Charles’ law is also known as the law of volumes. This law describes the behaviour of the gas compound, in which how gases tend to expand when heated. This law stated that: when the pressure on a sample of a dry gas is constant, the Kelvin temperature and the volume will be directly related. Jacques Charles was the one who formulated the original law in his unpublished work from the 1780s.

Mathematical formula

We can express Charles’s law of volumes as follow:



V is the volume of the gas,
T is the temperature of the gas (in kelvins),
k is a constant.

From this point of view, we can conclude that Charles’s law describes how a gas expands as the temperature in the system increases; conversely, a decrease in temperature will lead to a decrease in volume.

To compare same substance under different conditions we can express it as follow:

V1 / T1 = V2 / T2

Example of application

We can use Charles Law to describe why our tyre explode if we left it too long under the sunlight. The sunlight will increase the heat of our gas molecules inside our tyre. As it gets hotter, the volume will also expand, creating a pressure to our tyre. If our tyre is not strong enough to exert the same pressure, then the tyre will explode. That’s why be careful of sunlight, won’t you? If you other people should learn about basic laws of chemistry, please do share this article!

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