Gay Lussac’s law and its applications

Scientist Joseph Louis Gay-Lussac experimented with a fixed volume of gas and observed the effect of change in pressure on the temperature of the gas. He found that the pressure is directly proportional to the temperature. When he increased the pressure of a fixed volume of gas, temperature of gas was increased.


When he plotted his findings in graphical form by putting pressure on Y axis and temperature on X axis, he found a straight line. And when he repeated his experiment with different volumes of gas, he again found straight lines but with different slopes. Each line of this graph is called isochore which means experiment is done under constant volume condition.

Gay Lussac’s law

You might have experienced​​ Gay Lussac’s law in hot summer days. Pressure in well inflated tyre is almost constant but when temperature increases in summer days it increases pressure and sometimes tyres may burst.


Do you know Gay Lussac’s law has also benefitted our defence services? Guns and other firing equipments are thrilling examples of Gay Lussac’s law. When gun pin strikes, it ignites the gun powder and this increases the temperature which in turn increases the pressure and bullet is fired from the gun. Gay Lussac’s law helps to fire bullet with higher pressure so it can travel longer with high speed, but if the loading chamber is not designed properly, the gun can burst due to increase in pressure.


Now you can understand why on the bottles of spray paint and deodorants there is a warning not to put even empty bottles in fire. Because on increasing the temperature they can burst due to increased pressure.


Gay Lussac’s law can be derived by Boyle’s and Charles law. So we have three basic laws which are given for gases, Avogadro law, Boyle’s and Charles law. If we combine the above three laws, we get a new equation. In the next post we will discuss about this new gas equation.​

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Applications of Charles Law

Scientist Jacques Charles has demonstrated that the volume of gases increases with the rise in temperature and vice versa. He used his law to make a hot air balloon.

We encounter his law many times in our daily life. Let’s start with a very simple example; soda-can, when you open a chilled can you merely see bubbles but if you open a little warmer can, bubbles spill out the drink. Why do you think this happens? Definitely because of Charles’ law. In a warmer can volume of gases increases and as you open the can gas molecules find their way out.

Applications of Charles Law

Bread and delicious cakes are also gifts of Charles’ law. In bakery products yeast is used for fermentation. Yeast produces CO₂ and when we bake bread/ cake CO₂ expands due to increasing temperature and gives fluffiness to our bread and cakes.

If you want to witness Charles’ law, you can do an experiment with balloon yourself. Choose a sunny day for your experiment, go outside in warmer temperature and fill a balloon with gas. Then take it to a colder place. You will see your balloon shrinking in size as you place it in colder place and resuming its original size as you go outside. In a colder place, volume of gas reduces which results in shrinking of balloon. When you head outside, temperature increases and so does the volume of gas, so the balloon regains its size.

Sometimes we have to be alert from the effects of this law. Have you read the cautions written in the deodorant bottle? They suggest storing it below 50°C and also warn to keep it away from direct sun light and ignition. Because in higher temperature, volume of gases increases and if it reaches to the limit it can burst the bottle.


Now you can understand why in summer season chances of bursting of tyre tubes increases. This law also affects our body. In summer our lungs are filled with a larger volume of air as compared to the volume filled in winter. That’s why we can perform physical activity better in warmer days. Another scientist Joseph Gay-Lussac studied the effect of pressure on the temperature of gas. In the next post we will study his findings. 

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Gas Laws: Charles’ law

Scientist Jacques Charles experimented with a fixed amount of gas at constant pressure, when he increased the temperature of the gas, he found that the volume of gas was increased and the volume of gas decreased with decrease in temperature.

He repeated his experiment with a number of gases and every time he found the same behaviour. When he drew the graph between volume and temperature, he found a straight line. He concluded that the volume of a gas is directly proportional to the temperature.

Graphs of Charles’ law 

Then he repeated his experiment at a different pressure, this time also he found a straight line but with different slope. He found that with increasing the pressure the slop of straight line decreased, which means gases disobeyed his law at higher pressure.

Charles observed that the volume of gas decreased with decrease in temperature, so he was curious to find out what happens below zero degree. But at his time it was practically difficult to maintain such a lower temperature for this experiment. So he decided to do it mathematically.  When he extrapolated the straight line obtained by V vs T graph, he found that all lines meet the temperature axis at -273.15°C.

Although the volume of gas decreased with decrease in temperature, it was impossible to obtain a negative volume corresponding to the negative temperature, because negative volume means gas doesn’t exist. On the basis of Charles law, the new scale of temperature was developed by Kelvin. In Kelvin scale temperature is given by (t°C+ 273.15)K.

And the imaginary temperature, at which according to Charles the volume of all gases is supposed to be zero, is defined as absolute zero in Kelvin scale.

In our next post we will see how we get benefited by his discovery.  

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Boyel’s Law and Its Applications

In the last post we have studied the Boyel's law. In his experiment Robert Boyle showed that when a gas gets compressed, same number of molecules come closer and get fitted in a smaller volume. If we increase pressure twice, the volume of gas decreases to half.

Do you know we encounter Boyel’s law many times in our daily life? Science is everywhere around us and we use it all the time knowingly or unknowingly. 

Did you ever try to fill air in the tube of your cycle by mouth? Why couldn’t you succeed in that? And why it can be done so easily when you use a pump. Because by mouth you couldn’t create enough pressure to push air in the smaller volume of tube but when you use pump it exerts extra pressure and forces air to fill in a smaller volume.

We use this law in water guns and syringes. To understand how, you have to review the law to see how pressure and volume counter act each other. If pressure is increased, it decreases the volume and vice versa. When you pull the lever to fill water/liquid, it decreases the pressure inside which results in increase in volume, so higher number of molecules can be filled in it. And when you push the lever, you exert pressure which decreases the volume and molecules are forced out of the gun/syringe through its opening.

Now you can find more examples from your daily life. Deodorant spray, spray paints are also using boyel’s law. As you press the nozzle, it eases pressure and increases volume which causes molecules to come out forcefully.   

Our body uses this simple phenomenon 24 hours a day. Yes, your guess is correct, breathing. Every time we breathe, our lungs expand by contraction of diaphragm, which increases volume and decreases pressure inside the lung, this causes air to rush in at the time of inhalation. For exhalation, diaphragm relaxes, reducing the volume of lungs, which increases the pressure and causes air to get expelled from the lungs.

This knowledge can save your life when you go for deep sea diving, let’s see how. Our body is accustomed to live in atmospheric pressure, atmospheric pressure increases when you go deep in water which adds pressure of water too. If you descend slowly, your body can manage the change in pressure but when you descend quickly, sudden increase in pressure causes decrease the volume and nitrogen molecules start getting absorbed in blood. And when you ascent quickly, these nitrogen molecule try to escape and any built up nitrogen between the diver's joints will also want to expand. This causes the diver to bend over and experience severe pain.

Another scientist Charles experimented to see the effect of temperature on volume of gas at constant pressure. In our next post we will see how his experiment leads us to a trip on hot air balloon.

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Gas Laws: Boyle’s Law

You have become quite familiar with the atoms and molecules. These atoms and their interactions make matter. We are surrounded by three kinds of matter; gas, liquid and solid. Gas is the simplest form of matter, it is formed by atoms or molecules which are randomly moving around. When they are forced to come closer they form liquid phase, in this state of matter molecules have a few boundations, like they have to move together. And when these molecules are forced to have a much disciplined behaviour, they make the solid state of matter. Here molecules are much disciplined, just like an army battalion.
In this post we will explore properties of gases. Let’s list out the properties of gases that we know:

• We can fill a gas in any vessel as it has no shape,
• We can compress a gas,
• Gases have lower density than liquids and solids,
• We can mix gases without using any stirrer,
• Gases exert pressure evenly.

Now we will see what the scientists have discovered about gases. Scientists experimented with gases and found out how they behave with changing temperature, pressure and volume. There are four variables; number of moles of the gas, temperature, pressure and volume. If you want to find the relation between any two of them, you have to keep the other two constant.

Robert Boyle experimented with the compressible nature of gas. He took a fixed amount of gas at a constant temperature, then compressed it by increasing pressure on it and observed the change in volume occupied by the gas.

In his experiment, he found that when he increased pressure, the gas became compressed and the volume occupied by the gas was decreased. Mathematically, he found that, the pressure is inversely proportional to the volume. When he represented his findings in a graph where he put Pressure in y axis and volume at x axis. He found a curve.

Graphs of Boyle's law

And when he repeated his experiment at different temperatures he found graphs with different curves, so he came to the conclusion that the product of pressure and volume is a constant but this constant is different for a given set of temperature and amount of the gas. That’s why he found different curves in (P vs V) graphs for different temperatures.

In the next post we will discuss more about Boyel’s experiments and see what did he concluded with his experiments and how do we get benefitted with his findings. 

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What is Avogadro's Hypothesis?

You have learnt in the previous post that one mole of any substance contains 6.022×10²³ number of entities. Today we will try to find out how this number comes into picture.

Scientists needed to determine the weight of any element relative to a standard element, so they chose Carbon as standard element to determine the mass of atom and the number of atoms present in a mole. They choose Carbon ¹²C because its atomic weight is a whole number 12 atomic mass unit.

They measured the weight of one atom of Carbon spectroscopically. Then they used it to find the number of atoms present in the one mole i.e. 12g of carbon. Thus they got the number 6.022×10²³, and named it Avogadro Constant in honour of Avogadro

Avogadro proposed a hypothesis in which he said that equal volume of gases at the same temperature and pressure contains the same number of molecules. During his lifetime Avogadro's hypothesis was not well accepted but today it has become the base of mole concept.

Avogadro's hypothesis

This hypothesis is very simple to understand. Suppose you have to decorate a room for B’day party and for it you are filling air in balloons. If you want 4 balloons of equal size, then what you will do? Of course you fill them with equal amount of air. That means equal volume of air in the balloons contains equal number of molecules.

And if you want a few bigger balloons, then you will force more air to fill more air in the balloons. It’s obvious that larger volume contains more molecules. That means if you increase the volume, the number of molecules will increase. The number of molecules represents the number of moles. And mathematically you can say volume is directly proportional to the number of moles.

What is air? Air is the gaseous state of the molecules. Fascination towards air isn’t new, everyone has dreamed of flying in air, like birds. It motivates scientists to know more about it, that is why they continually experiment with it. Because of it today we are able to fly in air.

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Mole: A unit of measurement

You have learnt about atomic weight in the previous posts. And we can calculate molecular weight by simple addition of atomic weights of bonded atoms so why do we need another measuring unit?

For chemical recipes scientists need a common measuring unit like we use ‘Dozen’ for 12 items. For those they defined a new unit and named it ‘Mole’.

A mole of any substance contains similar number like 1 dozen apples contains 12 apple, 1 dozen bananas contains 12 bananas. A mole is equal to 6.022×10²³ items. It is a magical number and you are going to be amazed by its magic.

Can you answer these questions?

• How many atoms of carbon are present in a mole of carbon? 
• How many molecules are present in a mole of water? 

Do you know the answer of the above questions is the magical number 6.022×10²³. It is the master key for chemists and it is called the Avogadro constant and is denoted as N.

You have understood that one mole is equal to 6.022×10²³. But how do you measure a mole of a substance? We can't count those tiny atoms or molecules, can we? Don't worry, we don't have to. 

One mole is equal to the atomic weight of any element in grams. For examples: 1 mole Carbon is equal to the 12g, 1 mole Oxygen is equal to the 16g and 1 mole Hydrogen is equal to the 1g.

Similarly for molecules one mole is equal to their formula mass in grams. For example 1 mole water H₂O is equal to 2(atomic wt of Hydrogen) + atomic wt of Oxygen= 2g+16g=18g.

Now try to solve these puzzles:

• How many molecules of water are present in 18g of water? 
• How many atoms are present in 16g of Oxygen? 
• Is the number of atoms present in 1g Hydrogen equal to the number of atoms present in12g of Carbon?

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Intra-molecular Hydrogen Bond

You have seen that Hydrogen bond is formed between Hydrogen bond donor and Hydrogen bond accepter. If both of them are present in the same molecule and at a close distance, they can form Hydrogen bond. In this case it is called Intra-molecular Hydrogen Bond.

Let’s study it with a few examples, in acetylacetone molecule when you draw kekulé structure you will be able to distinguish Hydrogen bond donor and Hydrogen bond accepter. Hydrogen bond accepter C=O^δ- shares its lone pair with ^δ+H-O and makes Hydrogen bond.

Other example is salicylaldehyde, it also has Hydrogen bond accepter C=O^δ- which shares its lone pair with Hydrogen bond donor ^δ+H-O and makes Hydrogen bond. You have seen that if Hydrogen bond acceptor and donor both are present in the same molecule they are likely to form intra-molecular hydrogen bond. But in some molecules geometry doesn’t allow them to make hydrogen bond.

Let’s compare two different molecules which have similar groups at different position Ortho- nitro phenol and Para-nitro phenol. Both molecules have N-O^δ- and ^δ+H-O but in the latter molecule (para) the two groups are far apart, so they cannot form Hydrogen bond.

Hydrogen bonds are important for molecules as they affect a number of properties of molecules and they are important for our lives too. You know DNA and Proteins are crucial for our life. Hydrogen bonding gives them their unique structure and properties.

You may wonder how Hydrogen bonding affects the properties of molecules. Let’s try to understand it, Intermolecular hydrogen bonding binds together a number of molecules so it affects properties that depend on number of molecules like boiling point, melting point, viscosity etc. Intramolecular hydrogen bonding affects the property of that particular molecule like acidity, reactivity, stability.

You have learnt about elements and there relations and you have become familiar with molecules. In the coming posts we will study how molecules react and form a new molecule. We can neither count the number nor can we weigh as molecules are too small to see. So we will need a measuring unit that suits for electrons, atoms as well as molecules. In the next post we will learn about this measuring unit and see how it suits all of them.

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What are Hydrogen Bond Accepter and Hydrogen Bond Donor?

In this post we will see how it is possible for a molecule to form Hydrogen bonding even if it doesn’t have H directly bonded to an electronegative element. In order to find the reason behind it, we have to review Hydrogen bonding.

Hydrogen bond is formed between partially negative element and partially positive Hydrogen, in which, electronegative element of one molecule gives its lone pair of electrons to electron deficient Hydrogen of other molecule. That means, in this process one molecule acts as a donor and other behaves as an acceptor.

Same molecule can act both as a donor and an acceptor. Generally hydrogen bond donors are the molecules in which H is directly attached to electronegative element like H₂O, NH₃, HF, CH₃OH etc. and Hydrogen bond acceptors are the molecules that do not have H directly bonded to electronegative element like diethyl ether CH₃OCH₃.

Let’s take an example to understand it. If a molecule of H₂O comes closer to NH₃ molecule. There are two possibilities of Hydrogen bonding; either O of water donates its lone pair to the H of NH₃ or N of NH₃donates its lone pair to the H of water molecule. In the first case water accepts H from NH₃ and NH₃ acts as donor, while in the latter case they reverse the role of donor and acceptor. Which one will behave as a donor and an accepter depends solely on chance.

If a molecule of CH₃OCH₃ comes closer to the H₂O molecule, CH₃OCH₃ acts as Hydrogen bond accepter and H₂O acts as donor. Thus CH₃OCH₃ molecules make Hydrogen bonds with water molecules.

The quality of water to make Hydrogen bond with other molecules makes it universal solvent. Molecules which make Hydrogen bond with water are soluble in water.

In some conditions Hydrogen bond is formed inside the same molecule and it is called Intramolecular hydrogen bond. In the next post we will study the examples of Intramolecular hydrogen bonding.​

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