Gas Laws - WordPress.com · Gas Laws Book page 171 -173 Syllabus 5.15 – 5.17 05/09/2016 ©cgrahamphysics.com 2015

Gas Laws Book page 171 -173

Syllabus 5.15 – 5.17

©cgrahamphysics.com 2015 05/09/2016

What do all these have in common?

©cgrahamphysics.com 2015

Can you explain:

• How To Get A Egg Into A Bottle

• Rally Robin


How To Get A Egg Into A Bottle.mp4

1. Students number off.

2. Teachers asks a question and gives “think time”. (30 seconds)

3. Students privately write own answers [solo time]. (30 seconds)

4. Students stand up, put heads together [huddle up], show answers,

discuss, and coach if necessary.

5. Students sit down when everyone knows the answer or has

something they can share.

6. Teacher calls a number; that numbered student

from each group stands and simultaneously

answers the teacher’s question.

7. Teammates praise [CELEBRATE] students who

responded.

What do you think? • Is there a lowest temperature that you

can reach?

• If there is, why?

• What is temperature? What does it describe?

• How can you convert between Kelvin and Celsius


End 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

End 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Aim • Understand how temperature, pressure and

volume are related

Key words

• Boyle’s Law

• Charles’ Law

• Temperature Law

• Combined Gas Laws


Have you ever wondered?

If you pump up a tyre or ball, what happens to the amount of space the air takes up?

Keep volume constant


kT

PP

T

Temperature (K)

Pressure (torr)

k (torr/K)

248 691.6 2.79

273 760.0 2.78

298 828.4 2.78

373 1,041.2 2.79

Temperature Law



How does temperature affect pressure? • The higher the temperature of a gas, the greater the kinetic energy

of the particles. • They move faster and collide with the walls of the container more

frequently and with greater force.

• This increases the pressure of the gas when volume is constant.

Pressure and temperature are directly proportional.

higher temperature higher pressure

pressure (Pa) temperature (K)

= constant P1

T1 =

P2

T2


The Pressure-Temperature Law

A gas has a pressure of 1000 Pa at a temperature of 295 K.

What is the pressure when it is heated to 395 K?

P1

T1

P2 =

P2 =

P2 = 1339 Pa

P2

T2 =

× T2

P1

T1

1000 295 × 395

Keep temperature constant


P

V PV = k

Volume (mL)

Pressure (torr)

k (mL·torr)

10.0 760.0 7.60 x 103

20.0 379.6 7.59 x 103

30.0 253.2 7.60 x 103

40.0 191.0 7.64 x 103

Boyle’s Law



How does volume affect pressure?

P1 × V1 = P2 × V2

When the temperature of a gas is kept constant, a change in volume causes a change in pressure.

Particles collide more frequently with the container wall when the volume is smaller. This increases the pressure.

larger volume lower pressure

Pressure and volume are inversely proportional.

pressure (Pa) × volume (m3) = constant

Students take turns writing on own paper then pass it on

to teammates:

1. Teacher announces topic / gives “think time”.

2. Each teammate writes his/her short answer to

the topic on own paper then passes the paper

on to the next teammate.

3. Writing continues until the teacher

says stop.

Boyle’s Law


• Can you explain why?

• Balloon in the vacuum pump.mp4

Balloon in the vacuum pump.mp4


Boyle’s Law Example:

A gas syringe contains 0.00005 m3 of CO2 at a pressure of

100 kPa. If the volume is reduced to 0.000035 m3, what is the

new pressure?

P1 × V1 = P2 × V2

P1 × V1

V2

100,000 × 0.00005 0.000035

P2 = 143 kPa

P2 =

P2 =

Keep Pressure constant


kT

V

V

T

Volume (mL)

Temperature (K)

k (mL/K)

40.0 273.2 0.146

44.0 298.2 0.148

47.7 323.2 0.148

51.3 348.2 0.147

Charles’s Law


Charles’s Law

• Charles' Law

• Can you explain what happened?

• Simultaneous Round table


Charles' Law - Balloon blown-up in a Flask.mp4


How does temperature affect volume? • If a gas is in a container that does not have a fixed volume, then it

will expand as it is heated. • The pressure on the walls of the container will cause it to expand,

so pressure stays constant. higher temperature larger volume

Temperature and volume are directly proportional.

V1

T1

volume (m3) temperature (K)

= constant V2

T2

=


Charles’ Law

Example:

A gas has an initial temperature of 300 K and initial volume of

0.2 m3. What is the volume when it is heated to 330 K?

V1

T1

V2 =

V2 =

V2 = 0.22 m3

= V2

T2

× T2

V1

T1

× 330 0.2

300


The Combined Gas Law The Combined Gas Law brings together the Pressure-

Temperature Law, Boyle’s Law and Charles’ Law.

It is generally written as:

pressure × volume

temperature

To compare the behaviour of a gas in different conditions,

the following form of the equation is used:

P1V1 T1

It describes the relationship between volume, pressure and temperature, whether or not any variable is kept fixed.

= constant

P2V2 T2

=

Gas Law Problems • A gas has an initial temperature of 3 oC and occupies an initial

volume of 100 mL at 150kPa. Find its new volume when its pressure changes to 200 kPa and the temperature is changed to 8 oC.

Solution

• 𝑃1= 150kPa and 𝑃2 = 200 kPa

• 𝑇1 = 3 oC and 𝑇2 = 8 oC

• 𝑉1 = 100 mL and 𝑉2 = ?

•𝑃1𝑥𝑉1

𝑇1=

𝑃2𝑥 𝑉2

𝑇2 solve for 𝑉2


𝑉2 =𝑃1𝑥𝑉1

𝑇1 x

𝑇2

𝑃2

Convert 𝐶0 𝑡𝑜 𝐾𝑒𝑙𝑣𝑖𝑛: 𝑇1 = 273 + 3 = 276K 𝑇2 = 273 + 8 = 281K

Plug in numbers:

𝑉2= 150𝑥100𝑥281

276𝑥200= 76.35 𝑚𝐿

Gas Law Problems

• A gas pressure is 765 torr at 296 K. At what temperature will the pressure be 560 torr if the volume is held constant?

Solution

•𝑃1

𝑇1=

𝑃2

𝑇2

• 𝑇2 = 𝑃2𝑥𝑇1

𝑃1


𝑇2 =560𝑥296

765= 216.68𝐾

Given: 𝑃1 = 765 torr 𝑃2= 560 torr 𝑇1= 296 K 𝑇2 = ?


Using the Combined Gas Law


Plenary - Gas laws summary

Key words • Boyle’s Law - For a fixed amount of an ideal gas kept at a fixed

temperature, pressure and volume are inversely proportional.

• Charles’ Law – "For a fixed mass of gas, at a constant pressure, the volume is directly proportional to the absolute temperature."

• Pressure - temperature Law – It states that, for a given mass and constant volume of an ideal gas, the pressure exerted on the sides of its container is directly to its absolute temperature.

• Combined Gas Laws - Pressure is inversely proportional to volume, or higher volume equals lower pressure. Pressure is directly proportional to temperature, or higher temperature equals higher pressure.


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Gas Laws - WordPress.com · Gas Laws Book page 171 -173 Syllabus 5.15 – 5.17 05/09/2016 ©cgrahamphysics.com 2015