Henry's Law and Gas Solubility Explained

Summary

This script explores Henry's Law, demonstrating how gas solubility in a liquid is affected by pressure. Using carbon dioxide in water, it shows that doubling the pressure quadruples solubility. The script applies Henry's Law to predict how much CO2 escapes from an opened soda bottle, illustrating a practical application of the law in everyday life.

Takeaways

• 🧪 The pressure of a gas above a liquid affects its solubility in that liquid.
• 📦 Experiments with equal-sized vessels demonstrate how pressure impacts gas solubility.
• 🌐 Henry's Law states that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas.
• 📉 As pressure increases, the solubility of a gas in a liquid doubles with each doubling of pressure.
• 🌿 The example of carbon dioxide dissolving in water is used to illustrate Henry's Law.
• 🥤 Soda bottles are pressurized with carbon dioxide to keep the bubbles dissolved until opened.
• 💨 When a soda bottle is opened, the pressure of CO2 drops, leading to the release of gas and the soda going flat.
• 🔍 Henry's Law constant for CO2 is used to calculate the expected amount of gas that will escape from an opened soda.
• 📏 A calculation shows that approximately 2.7 liters of CO2 will escape from a 1-liter soda over a few hours.
• 🔬 A modern trick allows observing the gas release effect without waiting for the soda to go flat naturally.

Q & A

What is the relationship between the pressure of a gas above a liquid and its solubility?

The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid, as described by Henry's Law.

What is Henry's Law?

Henry's Law states that the solubility of a gas in a liquid is equal to the product of Henry's constant for that gas and the partial pressure of the gas above the liquid.

How does the experiment with three vessels of water and varying amounts of CO2 demonstrate Henry's Law?

The experiment shows that doubling the pressure of CO2 above the water doubles the solubility of CO2 in the water, illustrating a linear relationship between pressure and solubility.

What is the role of Henry's constant in Henry's Law?

Henry's constant is a proportionality constant that relates the solubility of a specific gas to its partial pressure in a solution at a given temperature.

Why does the amount of gas dissolved in soda decrease when the bottle is opened?

When a soda bottle is opened, the pressure of CO2 decreases significantly, leading to a decrease in solubility according to Henry's Law, causing the gas to effervesce.

What is the typical pressure of CO2 in a closed soda bottle?

The typical pressure of CO2 in a closed soda bottle is about 4.0 atmospheres.

How is the solubility of CO2 in water calculated using Henry's Law?

The solubility of CO2 in water is calculated by multiplying Henry's constant for CO2 (3.1 x 10^-2 mole per liter atmosphere) by the partial pressure of CO2 (4 atmospheres in a closed bottle).

What happens to the solubility of CO2 in soda when the bottle is opened?

When the soda bottle is opened, the partial pressure of CO2 drops to nearly zero, resulting in a significant decrease in CO2 solubility.

How much CO2 is expected to escape from a soda bottle once it's been opened?

About 2.7 liters of CO2 is expected to escape from a 1-liter soda bottle once it's been opened, based on the calculation using Henry's Law.

What is the significance of the Henry's Law constant being a constant?

The Henry's Law constant being a constant allows for the prediction of gas solubility changes with pressure changes, as it does not vary with pressure.

What is the practical application of understanding the relationship between gas pressure and solubility in beverages like soda?

Understanding this relationship is crucial for maintaining the fizz in carbonated beverages and for the design of processes that involve gas dissolution, such as in soft drink production.

Outlines

00:00

🧪 Henry's Law and Gas Solubility

This paragraph discusses the relationship between the pressure of a gas above a liquid and the solubility of that gas in the liquid. The presenter uses three equal-sized vessels with water, leaving headspace to introduce carbon dioxide (CO2) at varying pressures. It is explained that doubling the pressure of CO2 also doubles its solubility in water, following Henry's Law. The law states that the solubility of a gas is equal to Henry's constant multiplied by the partial pressure of the gas. The presenter then applies Henry's Law to predict the amount of CO2 that escapes from a soda bottle when opened, showing how the solubility of CO2 decreases dramatically when the pressure drops from 4 atmospheres to near zero.

05:01

🌌 Chemistry in Our Universe

The second paragraph introduces the presenter's new project, a 60-lecture course in general chemistry named 'Chemistry in Our Universe'. The course is produced in collaboration with 'Two Great Courses'. The presenter invites viewers to learn more about the project by visiting the website and searching for the course. The presenter also directs viewers to their YouTube channel for more content, and the paragraph ends with musical and applause elements, suggesting a lively and engaging presentation style.

Keywords

💡Pressure

Pressure is defined as the force exerted by a gas or liquid against a surface. In the context of the video, it is discussed as the force exerted by a gas above a liquid, which can affect the solubility of the gas in the liquid. The video uses the example of carbon dioxide gas above water to illustrate how increasing pressure increases the solubility of the gas in the liquid.

💡Solubility

Solubility refers to the ability of a substance (solute) to dissolve in a solvent. The video explains how the solubility of a gas in a liquid is directly affected by the pressure of the gas above the liquid. It demonstrates that as the pressure of carbon dioxide above water increases, so does its solubility in the water.

💡Henry's Law

Henry's Law is a principle in physical chemistry that states that the amount of a given gas that dissolves in a liquid is directly proportional to the partial pressure of the gas. The video uses Henry's Law to explain the relationship between the pressure of a gas and its solubility in a liquid. It shows how doubling the pressure of carbon dioxide doubles its solubility in water.

💡Headspace

Headspace refers to the unfilled space above a liquid in a container. In the video, the concept of headspace is used to describe the area above the water in the vessels where gas can be introduced to vary the pressure. This is crucial for demonstrating the effect of pressure on gas solubility.

💡Carbon Dioxide

Carbon dioxide (CO2) is a chemical compound consisting of one carbon atom double-bonded to two oxygen atoms. It is used in the video as an example of a gas that can dissolve in water. The video discusses how varying the pressure of CO2 above water affects its solubility.

💡Ideal Gas Law

The Ideal Gas Law is a principle that describes the behavior of an ideal gas under varying conditions of temperature, pressure, and volume. The video mentions the Ideal Gas Law to explain how doubling the number of moles of gas in a given volume at constant temperature results in doubling the pressure.

💡Partial Pressure

Partial Pressure is the pressure exerted by a specific gas in a mixture of gases. In the context of the video, it is used to describe the pressure of carbon dioxide in a closed soda bottle. The video explains how the partial pressure of CO2 affects its solubility in the soda.

💡Henry's Constant

Henry's Constant is a proportionality constant that relates the solubility of a gas in a solvent to the partial pressure of the gas. The video uses the Henry's Constant for carbon dioxide to calculate its solubility under different pressures. It is a key component in applying Henry's Law.

💡Effervescence

Effervescence refers to the formation and escape of bubbles in a liquid, typically due to the release of a dissolved gas. The video discusses how, when a soda bottle is opened, the pressure of carbon dioxide decreases, leading to a decrease in its solubility and the subsequent effervescence of CO2.

💡Moles

Moles are a unit of measurement used in chemistry to express amounts of a chemical substance. The video uses the concept of moles to quantify the amount of carbon dioxide that can dissolve in a liter of water under different pressures, demonstrating the relationship between pressure and solubility.

💡Atmosphere

An atmosphere is a unit of pressure equal to the pressure of Earth's atmosphere at sea level. The video uses the term 'atmosphere' to describe the pressure of carbon dioxide in a closed soda bottle and how it changes when the bottle is opened.

Highlights

The pressure of a gas above a liquid can affect its solubility in that liquid.

Using three equal-sized vessels to demonstrate the effect of gas pressure on solubility.

Leaving headspace in the vessels to add gas samples.

Carbon dioxide is used as the gas sample to test solubility.

Doubling the amount of CO2 in each subsequent vessel to double the pressure.

As pressure doubles, solubility also doubles, following a linear mathematical relationship.

Introducing Henry's Law, which states that gas solubility is equal to Henry's constant times the partial pressure of the gas.

Henry's Law allows predicting gas solubility as it is pressurized or depressurized.

Using Henry's Law to solve a problem involving a soda bottle pressurized with carbon dioxide.

The headspace inside a soda bottle typically has about 4.0 atmospheres of pure carbon dioxide.

Upon opening a soda bottle, carbon dioxide escapes due to the drop in pressure.

Calculating the solubility of CO2 using Henry's Law constant and the partial pressure in a closed bottle.

The Henry's Law constant for carbon dioxide is 3.1 times 10 to the minus 2 mole per liter atmosphere.

The solubility of CO2 in water under 4 atmospheres of pressure is calculated to be 1.2 times 10 to the minus 1 moles per liter.

After opening the bottle, the solubility of CO2 drops significantly due to the pressure decrease.

The new solubility of CO2 in soda after opening is only 1.2 times 10 to the minus 5 moles per liter.

Assuming all the initially soluble CO2 will escape, about 2.7 liters of carbon dioxide will be released from a 1-liter soda.

A trick to observe the CO2 release effect without waiting is mentioned, to be explored later.

The clip is from a project called 'Chemistry in Our Universe', a 60-lecture course in general chemistry.

The project is produced in collaboration with 'The Great Courses'.

Transcripts

let's take a little bit of time and

think about how the pressure of a gas

above a liquid can affect its solubility

in that liquid to do this I'm going to

use three vessels equal in size I'm

going to add to them equal volumes of

water as well but this time I'm not

going to fill them all the way to the

top I'm going to leave some headspace

available here now let's imagine that in

that headspace I can place a sample of

gas and I can make that gas as high or

low pressure as I choose in this case

we'll do carbon dioxide in

my leftmost vessel I'm going to put a

small amount of co2 so whatever pressure

this may correspond to let's double that

in the second vessel so twice as many

moles of gas in the same volume the same

temperature should give me double the

pressure for our ideal gas law

let's do it one more time we'll double

the pressure yet again in our third

vessel by adding another equivalent of

our co2 now if we were to look at the

solutions beneath these head spaces that

are filled with gas at various pressures

we would find different amounts of that

gas dissolved inside of that solution in

fact what we would find is that as we

double the pressure each time we also

double the solubility notice that here

I've gone from two to four to ultimately

eight depending upon how much of this

stuff I've done so each time I double

the pressure I double the solubility

that is a linear mathematical

relationship and it's a very simple

equation that leads to a very powerful

law Henry's law the equation is the

solubility of a gas is

equal to a constant called Henry's

constant times the partial pressure of

that gas now since I've been using pure

gases in my example here the partial

pressure of the gas would be the total

pressure of that gas within the system

and nothing else but Henry's law is

really quite interesting in hell it

allows us to predict the solubility of a

gas and how it will vary as we

pressurize and depressurize that gas

above the solution so let's put Henry's

law to use and solve a problem

soda bottled under an atmosphere of

carbon dioxide gas in order to keep the

bubbles dissolved into the soda before

you open it now typically that headspace

inside of your soda has a pressure of

about 4.0 atmospheres of pure carbon

dioxide so when you open the bottle you

hear that rush of gas escaping that's

the four atmosphere of carbon dioxide

escaping the bottle now ordinary

atmospheric gases rush back in but the

partial pressure of carbon dioxide drops

to practically nothing so the question

we're going to ask here is this how much

gas can we expect to effervesce from a

soda once it's been opened total of all

the gas were to escape at once how much

would we get well let's figure that out

to answer the question we're going to

use Henry's law and in order to use

Henry's law we have to go to a table and

find the Henry's law constant for carbon

dioxide now we can calculate the

solubility of co2 under that atmost at

four atmosphere pressure of carbon

dioxide

we're going to have to use a Henry's law

constant of 3.1 times 10 to the minus 2

mole per liter atmosphere and we're

going to multiply that by the partial

pressure of co2 in this case 4

atmospheres in a closed bottle a quick

unit analysis lets me know that I've got

the equation right I'm going to get an

answer of moles per liter and

in this case it comes out to 1.2 times

10 to the minus 1 moles per liter that's

the total amount of carbon dioxide

that's soluble in water under an

atmosphere of 4 atmosphere carbon

dioxide

but once that bottle is open something

changes namely the pressure notice that

the Henry's law constant does not change

that's why it's a constant but the

pressure has dropped all the way down to

practically nothing about 4 times 10 to

the minus 4 atmospheres a factor of

10,000 difference meaning that the new

solubility of co2 in your soda is only

1.2 times 10 to the minus 5 moles per

liter now that's so low that it's

negligible so let's finish our problem

by assuming that all of the 1.2 times 10

to the minus 1 molar co2 will be

escaping

well 1.2 times 10 to the minus minus one

moles coming from a 1 liter solution at

standard temperature and pressure we

know should occupy 20 2.4 liters so when

we do the math here we get our leaders

for our units we discover that about 2.7

liters of carbon dioxide will escape

slowly and lazily from your soda as it

goes flat over the period of a few hours

now there's a really great trick that's

become popular in recent years it allows

you to observe that effect without

having to wait we'll check that one out

in just a minute the preceding is a clip

from my new project entitled chemistry

in our universe how it all works a 60

lecture course in general chemistry

produced in collaboration with two great

courses to learn more about this project

go to WWE our courses comm and search

chemistry and our universe to learn more

about me check out my youtube channel at

youtube.com slash chem survival

[Music]

[Applause]

[Music]

you

[Music]