Chemistry: Gay-Lussac’s Law (Gas Laws) with 2 examples | Homework Tutor

For a gas, temperature and pressure are directly
proportional. When you keep everything else constant, as the temperature of a gas goes
up, its pressure goes up. As the temperature of a gas goes down, its pressure goes down. If you heat up a gas, the gas particles move
faster. If the gas is in a solid container, with fixed volume, this means that the faster
the gas particles move, the more times per second they collide with the sides of the
container. That registers as increased pressure. The converse is also true – if you cool down
this container of gas, that means the gas particles are moving more slowly. So there
will be fewer collisions with the sides of the container per second, which means lower
pressure. Joseph Louis Gay-Lussac shares credit with
Guillaume Amontons for establishing a Gas Law describing the relationship between temperature
and pressure. Gay-Lussac’s Law says that when the volume and amount of gas is constant,
pressure and temperature are directly proportional. P ∝ T You can write this mathematically
as P = kT where P = pressure,
T = temperature in Kelvin, and k = is a proportionality constant.
We can rearrange this equation so it reads P/T = k, or the ratio of pressure to temperature
is a constant, k. Very often, Gay-Lussac’s law is used to
compare two situations, a “before” and an “after.” In that case, you can say
P1 / T1= k, and P2 / T2 = k, so you can write Gay-Lussac’s law as
P1 / T1= P2 / T2. Let’s see an example. Example 1: A canister of nitrogen gas has
a pressure of 2000 psi (pounds per square inch) at 20 C°. What will the pressure be
if you increase the temperature to 25 C° ? Let’s write down Gay-Lussac’s Law: P1/ T1= P2 / T2, because we have a “before”
and “after.” Convert temperatures to Kelvin: Kelvin = C°+ 273.15. T1 = 293.15 K, T2 = 298.15 K
Substitute in what we know: 2000 psi / 293.15K = P2/ 298.15 K Solve for P2 (multiply both sides
by 298.15 K) P2 = (2000 psi )(298.15 K)/293.15 K P2 = 2034 psi Example 2. Here’s another example: At 10
C°, a gas exerts 0.95 atm of pressure. At what temperature (in Celsius) will it exert
a pressure of 0.75 atm? P1 /T1= P2/T2.
Convert temperatures to Kelvin: Kelvin = C°+ 273.15.
T1 = 283.15 K 0.95 atm/ 283.15 K = 0.75 atm/T2
Solve for T2 T2 = (283.15 K)(0.75 atm)/0.95 atm
T2 = 223.54 K Convert to Celsius: 223.54K – 273.15 = – 49.6 C° Gay-Lussac’s Law relates temperature and
pressure for a gas, but there are other gas laws which relate the other essential variables
associated with a gas. Charles’s Law is the relationship between temperature and volume.
Boyle’s Law is the relationship between pressure and volume. And the combined gas
law puts all 3 together: Temperature, Pressure, and Volume. Notice that to use any of these
laws, the amount of gas must be constant. Avogadro’s Law describes the relationship
between volume and the amount of a gas (usually in terms of n, the number of moles). When
we combine all 4 laws, we get the Ideal Gas Law. To decide which of these gas laws to
use when solving a problem, make a list of what information you have, and what information
you need. If a variable doesn’t come up, or is held constant in the problem, you don’t
need it in your equation.

62 comments

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  2. Thank you so much for the awesome video! It's short and sweet yet makes us students grasp the concept very well! 😀

  3. Hello for the sake of clarification i will make the following argument and please correct me. You mentioned that the frequency of the gas particles colliding with the walls of the confinement registered as pressure and i say that is not true. I think what we ought to say is the faster they move around is the more intense they will bombard the walls of the container, hence the force is large compared to when they are moving slowly. The pressure equation does not account for frequency of collisions, rather the force exerted on the walls of the container, and the inner surface area of such a container.

  4. Very good videos indeed! I like their simplicity and the clarity used the illustration of the concepts. I have some suggestions though:
    – Attention should be paid on the units used to resolves exercises and I think SI units would be better since these videos are used internationally. Example pressure units (psi or atm) should be converted into Pascal (Pa).
    It would me worth mentioning that these processes are alo called isoprocesses (isothermal, isochoric, isobaric).

  5. Your voice, oh my gosh. I have to watch these videos for a class of mine and your voice reminds me of Haruhi Fujioka from the anime 'Ouran High School Host Club'.

  6. The examples were too easy. Give a tough one next time, just to clear out all the doubts in the same question.
    BTW, nice video 🙂 and an awesome voice.

  7. I live in Myanmar. I am very interesting your science tutorials. Please let me know which software you use for tutorial? Thank..:)

  8. how to visualise the reverse, i.e Increasing Temperature with increasing Pressure, keeping Volume and Mass constant ?

  9. can i copy the your video,but no all the full video i only copy the container with molecules inside(before and after) and they are moving can i copy?……because i need that for my project in science(video lesson)

  10. I have a question for u
    Is pressure is directly proptional to temperate
    Then in atmosphere why is pressure inversely proportional to temperature
    And your vedio was great

  11. When I was in school I used to confuse about these Gas laws. Now it is very clear. Thank you and continue making such useful videos.

  12. I never understood what is the meaning of properties of the elements repeats at regular intervals in the modern periodic table. Can u explain with example kindly

  13. Mam u are gojesh…..wonderful…. absolutely good..u. r mam…..u r ncee..Etc……because mam….1 hrs se ishi topic Ko clear lens chahti thi bt kise v channel k video se smjh nii aaya…. Mam you are very good teacher ………for chemistry…

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