Chapter 05: Gases Flashcards Preview

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1

Pressure

The force exerted per unit area by gas molecules as they strike the surfaces around them

Pressure = force/area = F/A

2

Pressure units & conversion factors

760 mmHg = 760 torr = 1 atm = 101,325 Pa

3

Elements that exist as gases at 25°C and 1 atm

1A: H

5A: N

6A: O

7A: F, Cl

8A: (all)

4

Force (formula)

mass × acceleration

5

SI units of force and pressure

Force: 1 newton (N)

Pressure: 1 pascal (Pa)

6

Newton

1 newton = 1 kg×m/s2

7

Pascal

1 pascal = 1N/m2 = 1 kg/(m×s2)

8

Barometer

Atmospheric pressure measurment tool

Inverted tube of Hg over open dish of Hg;
height of Hg in mm is equal to atmospheric pressure

9

Manometer

Instrument used to measure pressure of gas trapped in container

Gas pressure is determined by difference in liquid levels in U-shaped tube

(Pressure is high if it pushes down on liquid;
low if it cannot push down on liquid)

10

Simple Gas Laws: Four* basic properties of a gas

P, pressure

V, volume

T, temperature (Kelvin)

t, temperature (°C)

n, amount in moles

11

Boyle's law

Inverse relationship between volume and pressure

*n is constant
*T is constant

P1V1 = P2V2

12

Charles' law

Direct relationship between volume and temperature (Kelvin).

*P is constant
*n is constant

V1 = V2
T1   T2

13

Avogadro's law

Direct relationship between volume and quantity (number of moles)

*P is constant
*T is constant

V1 = V2
n       n

14

Ideal Gas Law

How a hypothetical gas behaves

PV = nRT

Where R is the ideal gas constant

15

R, ideal gas constant

R = 0.08206 L atm/mol K

16

Molar volume

The volume occupied by one mole of a substance

17

Ideal gas molar volume

22.414 L at STP of an ideal gas

18

STP

standard temperature and pressure

pressure = 1 atm at STP

temperature = 0°C or 273.15 K at STP

19

Density of a gas (formula)

d = PM
       RT

Where d = density
P = pressure in atm
M = molar mass
R = gas constant
T = temperature in Kelvin

20

Molar mass of a gas (formula)

M = dRT
       P

Where M = molar mass
d = density
R = gas constant
T = temperature in Kelvin
P = pressure in atm

21

Dalton's law

Partial pressures, Pn

Pn = nnRT
            V

Ptotal = Px + Py + Pz

*volume and temperature are constant

22

Mole fraction

Xn = nn
             ntotal

Thus, with Dalton's law:
Pn = XnPtotal

23

Vapor pressure

The partial pressure of water vapor in a system

24

Gas stoichiometry

General conceptual plan:

P, V, T / mass or volume of gas A --> moles of gas A -->
moles of gas B --> P, V, T / mass or volume of gas B

25

Kinetic molecular theory

1. Particle size is negligible, even those they have mass

2. Constant motion, random directions, no overall loss of energy, just a transfer of energy (known as being elastic)

3. Average kinetic energy is directly proportional to temperature in Kelvin

4. Gas particles exert neither attractive nor repulsive forces

26

Average kinetic energy

average kinetic energy = KE

( KE = 1/2×mv2 )

At same temperature, gases have same average kinetic energy

27

Boyle's law explained (KMT)

Decreasing volume forces gas particles into a smaller space, thus increasing collisions, and hence, pressure

*n and T are constant

28

Charle's law explained (KMT)

Temperature increase increases average kinetic energy

The higher the average kinetic energy, the greater the area particles will move around

Thus, volume increases

*P & n constant

29

Avogadro's law explained (KMT)

Increasing number of particles causes more collisions

To keep pressure constant, volume must then increase

*P and T are constant

30

Dalton's law explained (KMT)

Because average kinetic energy is the same (at same temperature), the total pressure of the collisions is the same