 We all must have seen how when we open a bottle of soda or a favourite cold beverage, small bubbles of gas start coming out, creating a very delightful fish or sometimes what looks like a magical effervescence, right? Now we also know that this gas that comes out of the carbonated drink is nothing but carbon dioxide gas bubbles. Now interesting thing is that the solubility of carbon dioxide in water is moderate at best, that is it has moderate solubility in water. So then how are we able to manage keeping so much carbon dioxide dissolved in our beverage drinks that as soon as you open we have this amazing fizzy experience? Well that's where Henry's Law comes into play. Yes, and that's what we are going to discuss in this video today. Henry's Law states that at a constant temperature the solubility of a gas is directly proportional to the partial pressure of the gas that is present above the surface of the liquid or solution. So that is to increase the solubility of carbon dioxide gas in a drink we have to increase its partial pressure and how do we do that? By increasing the pressure of carbonation. You see by increasing the pressure we increase the partial pressure of the gas. For example let's assume this is a container with a gas liquid mixture and this is the seal. Then if you have gas bubbles here by increasing the pressure we are forcing these gas particles to strike the liquid surface more often and the more number of gas particles strike the liquid surface greater will be its solubility. Now how much will the solubility increase like will the solubility increase indefinitely? Absolutely no. Solubility of the gas will increase until a new dynamic equilibrium is established where the number of gas particles entering the liquid is same as those that leave the solution face. So by applying Henry's law if we increase the pressure above the liquid the partial pressure of the carbon dioxide also increases and as a result the concentration of the dissolved carbon dioxide in the liquid increases proportionally. And this is why when you open a pressurized soda bottle you hear a fist because now the pressure has decreased such that the solubility of the dissolved carbon dioxide in the liquid decreases and all of that extra carbon dioxide that comes out of the solution goes out in the form of fist. Now how do we quantify Henry's law? Well if we use mold fraction as a measure of solubility so let's say mold fraction is x then mold fraction of the gas in the solution is directly proportional to the partial pressure of the gas that is above the solution. This is nothing but partial pressure of the gas is equal to k h into mold fraction of the gas. Now this k h is also called Henry's law constant. So if you take out this k h then you can see that it is inversely proportional to the mold fraction of the gas. So what does it mean? It means a gas that has higher value of k h will have lower value of solubility in a particular liquid. Different gases have different values of k h at the same temperature and this means that k h is also a function of the nature of a particular gas. Now interestingly for certain gases like nitrogen and oxygen this k h value is found to increase with temperature. With increase in temperature the solubility of these gases in water decreases because we are referring to water in this particular case. So it's also convenient that we keep a beverage drinks usually chilled because as we just saw in the case of nitrogen and oxygen solubility of gases in liquids generally decrease with increase in temperature. Keeping a beverage can chilled means the lower or the colder temperature also helps keep our carbon dioxide stay dissolved in the liquid. Henry's law has many such important applications in our everyday life like in beverage industry, food industry and so on. So let's go ahead and solve a few questions based on Henry's law in the next video.