Henry’s Law is a gas law which states that the amount of gas that is dissolved in a liquid is directly proportional to the partial pressure of that gas in the liquid at a given temperature. In other words: the more gas dissolved in a liquid, the more pressure that gas is exerting on its surroundings.
For instance, say you have carbon dioxide (CO2) bubbling through an area of water. The pressure of CO2 in the water will be higher than it would be if CO2 wasn’t dissolved, because it’s exerting more pressure to push against whatever is holding it back. This isn’t just relevant for science classes – Henry’s Law can help you design systems and understand how they work! It’s also one of those laws that can only be fully understood by breaking out your scientific calculator and setting up some equations. Which of the following should have the largest henry’s law constant (kh) in water?
•NH4+ (a positively charged ammonium ion)
•NO- (a negatively charged nitrate ion)
•SO42- (a negatively charged sulfate ion)
Oh, you’re right! The ammonium ion is the only one that has a charge to it, so it will be the most attracted to the oxygen in water, which will make it dissolve more in water than either of the other two ions. The other two are neutral and will dissolve less.
1. Henry’s Law can be reversed :
This is exactly the opposite effect that you learned about in your science classes! It may seem like Henry’s Law is a one-way street, but in reality it’s not. If you increase the temperature of water and dissolve CO2 into it, you can actually cause some of that CO2 to dissolve into the water and go away instead of staying inside! It turns out that if you have water at a hot temperature (around 30 or 40 degrees C) and dissolve CO2 into it, the solution will get rid of the dissolved gasses even at very low pressures.
This is called “spontaneous degassing” . It turns out that this happens because the solution will start to interact with and cool the CO2 molecules, sending some of them into the water. Some of these molecules quickly leave the solution and are not solvated (held in a specific place in space) any longer. These molecules then go through phase changes, which is exactly what happens when you put a glass under cold water – they turn from solid to liquid to gas.
2. Henry’s Law can be used in reverse to separate or enrich mixtures :
In this case, you’re still using Henry’s Law but would be using it in the opposite way that you usually see it. This is usually called “Gas Solubility Gradient Separation” (we’ll just call it GSS for now), and it works by having two chambers with different pressures separated by a membrane which allows the gas to flow through easily. In each chamber the pressure is different, and this causes gas to dissolve at a different rate in each solution, creating a gradient of gas concentration.
The most valuable part of this is that it can be used to separate mixtures, which is more effective than just by separating them based on mass or size. For example, if you have a mixture of two gasses and one of them is contaminating a certain area, you could use GSS to remove the contaminant without having to worry about it being mixed with other things. You would just have to take the contaminated area and push it through the GSS.
3. Henry’s Law can be used in reverse to create “artificial” solutions : .
If you take any gas you want to dissolve in water, put it under very low pressures and at temperatures below 30 degrees C, the gas will just spontaneously come out of the solution and separate from it! This is one of many ways that gasses can be separated from each other by doing a system of GSS. This process is called “decomposition” , and it’s actually what happens when foods spoil.
The decomposition process makes the gas come off naturally! This can be used by people in some extreme circumstances – for example in times when fresh air isn’t available. If you have a sealed space where you can’t get any oxygen, you could break the seal, give it a quick vacuum to remove most of the air, then use GSS to separate out the gas. It’s also useful for chemists who are looking for gasses in their laboratory.
4. Henry’s Law is a force that must be explained in newtons:
This applies to both your science class and your everyday life – Henry’s Law is a force which does not act in the same way that Newtonian physics says force should behave. In everyday life, people don’t pay attention to this effect because we’re used to forces acting in Newtonian ways – just like how gravity works.