section 13.1 describing the properties of gases 1.to learn about atmospheric pressure and how...

Section 13.1

Describing the Properties of Gases

1. To learn about atmospheric pressure and how barometers work

2. To learn the units of pressure

3. To understand how the pressure and volume of a gas are related

4. To do calculations involving Boyle’s Law

5. To learn about absolute zero

6. To understand how the volume and temperature of a gas are related

7. To do calculations involving Charles’s Law

8. To understand how the volume and number of moles of a gas are related

9. To do calculations involving Avogadro’s Law

10. To understand how the temperature and pressure of a gas are related.

11. To do calculations involving Gay-Lussac’s Law.

Objectives

Section 13.1


Units involved in Gas Laws (memorize these)

Volume• liters (L)• milliliters (mL)• centimeters cubed (cm3)• decimeters cubed (dm3)

Temperature• degrees Celsius (°C)• Kelvins (K)

– used primarily

Pressure• atmospheres (atm)• Pascals (Pa)• kilopascals (kPa)• pounds per square inch (psi)• millimeters of mercury (mmHg)• Torricellis (torr)

Standard Temperature & Pressure (STP)

• 0°C and 1 atmosphere

Section 13.1


• Barometer – device that measures atmospheric pressure– The weight of the air

pushing down on the open dish of mercury supports a column of mercury in a closed tube

Measuring Pressure

•Pressure – the force a gas exerts (per unit area) on its surroundings

•Gas pressure is caused by gas molecules colliding with the surfaces of the surrounding substances.

Section 13.1


A. Pressure

– Changing weather conditions

Atmospheric Pressure

Section 13.1


A. Pressure

– Changing altitude

Atmospheric Pressure

Section 13.1


A. Pressure

1 standard atmosphere of air pressure

= 1.000 atm

= 14.69 lbs / in2 (psi)

= 760.0 mm Hg

= 760.0 torr

= 101,325 Pa

= 101.325 kPa

Units of Pressure

Section 13.1


A. Pressure Measuring Pressure

• A manometer measures the pressure of a gas trapped in a container.

• What would the manometer look like if the gas pressure inside were equal to atmospheric pressure?

Section 13.1


• Robert Boyle’s experiment– a certain amount of gas

is trapped in a J-tube– as more mercury is

added, the trapped gas is compressed into a smaller volume• the same number of

gas molecules in a smaller volume = more frequent collisions

• Higher pressure

B. Pressure and Volume: Boyle’s Law(when temperature (T) and amount of gas (n) are constant!)

Section 13.1


B. Pressure and Volume: Boyle’s Law

Section 13.1


• Graphing Boyle’s results– as volume of the gas

increases the pressure on the gas decreases• more space = fewer

collisions

– as the volume of the gas decreases, pressure on the gas increases• smaller space =

more collisions


Section 13.1



• This graph has the shape of half of a hyperbola• Volume and pressure are inversely proportional.

– If one increases the other decreases.

more space=few collisions little space=more collisions

Section 13.1



Another way of stating Boyle’s Law is

P1V1 = P2V2

(constant temperature and amount of gas (moles))

Section 13.1


• When the pressure of a gas is kept constant– As the temperature increases, gas molecules travel

faster.– They collide with each other with much more force– The collision force them to bounce off each other a

greater distance– The gas molecules spread out a lot

• fill more volume

C. Volume and Temperature: Charles’s Law

Section 13.1


• Graphing data for several gases– as temperature increases,

volume increases• Temperature and Volume are

directly proportional to one another– if one increases, the other

also increases• T must be converted to Kelvins

C. Volume and Temperature: Charles’s Law(when pressure and amount of gas (moles) are constant!)

Section 13.1


• It is easier to write an equation for the relationship if we make the lines intersect the origin of the graph (0 and 0).– so we invented a new temperature scale (Kelvins)

• 0 Kelvins is called absolute zero

• At absolute zero, a gas has no volume (theoretically)


Section 13.1



• Volume and temperature are directly proportional. – If one increases the other increases.

• Another way of stating Charles’s Law is

• constant pressure (P) and amount of gas (n)• CAUTION: temperature must be expressed in Kelvins

(absolute temperature)• if not, convert it to Kelvins

• Ktemp = °Ctemp + 273

2

2

1

1

T

V

T

V=

Section 13.1


D. Volume and Moles: Avogadro’s Law(when temperature and pressure are constant!)

Section 13.1


D. Volume and Moles: Avogadro’s Law

• Volume of a gas is directly proportional to number of moles (amount) of gas

– If one increases the other increases. – at a constant temperature and pressure

• Another way of stating Avogadro’s Law is

(constant temperature and pressure)

2

2

1

1

n

V

n

V=

Section 13.1


E. Temperature and Pressure: Gay-Lussac’s Law(when volume and amount of gas (moles) are constant!)

Temperature and Pressure are directly proportional to one another.• As the temperature increases, gas molecules travel faster.• They collide with each other and the walls of the container more

often, and with greater force– more frequent & violent collisions = more pressure

2

2

1

1

T

P

T

P=

Section 13.1


• Pressure inversely proportional to Volume– Boyle’s Law

• Volume directly proportional to Absolute Temperature– Charles’s Law

• Volume directly proportional to Moles of gas– Avogadro’s Law

• Pressure directly proportional to Absolute Temperature– Gay-Lussac’s Law

Summary of Measurable Gas Properties

section 13.1 describing the properties of gases 1.to learn about atmospheric pressure and how...

Documents

pressure measuring pressure

surroundings gas pressure

kpa units of pressure

gas decreases

trapped gas

gas laws

boyles law slide

properties of gases