Pressure, Force and Area, Elevation, Boiling Point

Question 1

How do calculate/define pressure?

Answer 1

P = F/A
P = Pressure
F = Force
A = Area

Question 2

How can we calculate force in newtons from the mass of an object?

Answer 2

F = MG
F = Force
M = Mass
G = Gravitational Acceleration (9.8m/s^2)
Example: 5kg object is 5(9.8m/s^2) = 49N

Question 3

What is the standard unit of pressure? What does it represent?

Answer 3

Pascals (PA): It has the same value as 1 N/M^2 (Newtons per square metre) because 1 pascal is the same as if you exerted 1 newton of force on 1 square metre of area. The higher the pascal, the higher the force but not the area.

Question 4

How many kPA (kilopascal) is an atm (atmosphere)?

Answer 4

101.3 kPA = 1 atm

Question 5

How many torr are in an atm?

Answer 5

760 torr = 1 atm

Question 6

What does 1 torr represent?

Answer 6

1 torr is the same as 1 mm of Hg (mercury) of pressure

Question 7

What is the pressure at sea level?

Answer 7

1 atm

Question 8

How do elevation and pressure correlate?

Answer 8

As elevation goes up, pressure goes down. As elevation goes down, pressure goes up.
Example: At sea level it’s 1 atm while at the top a mountain it’s 0.52 atm.

Question 9

How to pressure and boiling point correlate?

Answer 9

As pressure goes up, boiling point goes up. As pressure goes down, boiling point goes down.
Example:
Water’s boiling point is 100c at 1 atm. At 0.5 atm, it’s 81.3, at 2 atm, it’s 120.8

Question 10

Why does the pressure lower with higher elevation?

Answer 10

Imagine at sea level that the sea is the area and all the air molecules exert weight. That’s all that air molecules over the area meaning higher pressure. The higher you go, the less air molecules over the same area, meaning lower pressure.

Question 11

Which is heavier, cold or hot air?

Answer 11

Cold air.

Question 12

Explain why certain gasses rise (water vapour, helium, Etc), while others fall (CO2, Argon, Etc)

Answer 12

The atmosphere is 78% N2 (28g/mol) and 21% O2 (32g/mol). CO2 is 44g/mol, making it heavy, making it fall. Water vapour is 18g/mol, making it lighter, making it rise. Another reason certain gasses rise or fall is dependant on their boiling point. Hot air tends to rise, while cold air tends to sink.

Average air is roughly 28.6g/mol

Question 13

Does a helium balloon expand or shrink as the elevation increases? Explain.

Answer 13

It expands. As it rises, the pressure being exerted on the outside of the balloon is less than the pressure on the inside, so the size will increase until the two pressures are equal.

Question 14

How do you convert between atmospheres (atms) and pounds per square inch (psi)?

Answer 14

1 atm = 14.7 psi

Question 15

In a manometer, you’re given the atmospheric pressure in mmHg (mm of mercury) and the height difference (in mmHg) between the atmospheric side and the gaseous side. Calculate the pressure of the gaseous side.

Answer 15

Whichever side is lower has a higher pressure. Given the information, if the the atmospheric side is higher (in mmHg), add the pressure and the height difference. If the height is lower, subtract the height difference from the atmospheric pressure.
Example:
If the pressure is 760 mmHg (1 atm) on the atmospheric side and is 60mmHg higher than the gaseous pressure, than the gaseous pressure is 820mmHg. If it was 60mmHg shorter, it would be 700mmHg.

Question 16

If you place an empty test tube in a container of mercury, does the mercury rise, fall or do nothing (assuming a consistent Patm of 1 atm)? Explain your answer.

Answer 16

The mercury does not rise or fall in the test tube. This is because there are gas particles creating a Patm of 760 acting on the surface of Hg liquid creating a balance.

Question 17

If you place a test tube with mercury inside it in a container of mercury, does the mercury rise, fall or do nothing (assuming a consistent Patm of 1 atm)? Explain your answer.

Answer 17

It depends, the mmHg in the test tube will rise or fall to match the Patm (atmospheric pressure). This is because the Hg displaces gas particles, so when you flip it over into a container, it retains the mmHg of pressure originally inside it. It naturally wants to match the Patm though so will rise or fall to match it.

Question 18

How do you find the height of water in a barometer given the density and column height of mercury and density of water in identical barometers?

Answer 18

First: Watm = Whg and Watm = Wh2o so Whg = Wh2o (W is weight, in other words, the weight of the atmosphere is balancing out the mercury and water in the barometer until equilibrium). Assuming they are in the same place, we can write the equation M1G = M2G (M = Mass and G = gravity, this is true because Whg = Wh2o and W = M*G). As density is M/V, we can rewrite the equation as D1V1 = D2V2, as a barometer is a cylinder and the volume of a cylinder is πr^2 * h, we can rewrite it as D1A1H1 = D2A2H2 (A = Area, H = Height). In an identical barometer, this is D1H1 = D2H2, now you just plug in both densities and the height of mercury to get the height of water.

The same is true for the opposite (find density from height)

All you really need to know is D1H1 = D2H2 and plug in the numbers in identical barometers and on identical planets. The rest is just how this equation is derived.

Question 19

What is Boyle’s Law and Boyle’s Law Formula?

Answer 19

As volume increase, pressure decreases, as pressure decreases, volume increases. The formula for this is P1V1 = P2V2

Question 20

What shape is Boyle’s Law Graph?

Answer 20

The graph looks curved as the graph seems to drop less and less (so a bigger drop at the beginning).

https://byjus.com/question-answer/how-do-you-graph-boyles-law/ if you would like to see what it looks like

Question 21

If you have two containers, one with high pressure the other with low pressure and connected the two containers, how does the air flow?

Answer 21

The one with higher pressure will naturally flow towards the one with lower pressure until equilibrium.

Question 22

What is Gay Lussac’s Law?

Answer 22

As temperature increases, pressure increases. As temperature decrease, pressure decreases.

P1/T1 = P2/T2