- #1

Gixer1127

- 28

- 12

- Homework Statement
- Looking for some pointers in where I am going wrong with this if possible please

- Relevant Equations
- pV=nRT pV = (m/Mr)RT)

Hey folks, any help will be greatly appreciated. I have, what I thought, was a fairly simple equation to follow to determine the mass of air in a pressurised air tank. See below question and my attempt at solving using the pV = (m/Mr)RT) equation.

A pressurised air tank supplies compressed air to a new hybrid air engine. When the hybrid engine is not running the absolute pressure in the tank is 320 bar and the temperature of the air is 50°C.

Using the General Gas Law: P1xV1/T1 = P2xV2/T2

Simplify the equation to P1/T1 = P2/T2 as there is no change to the volume.

Step 1) Convert the known temperature to Kelvin = T1 = 50⁰C + 273 = 323K

Insert values into the equation:

320/323 = 280/T2

T2 = (280/320) x 323 =282.62K

The temperature of the air in the high pressure air tank at 280 bar is 282.62K

Using the Characteristic Gas Law equation pV=nRT which can also be written as pV = (m/Mr)RT)

P is the pressure in Pa

V is the volume in m³

N is the amount of gas (in moles)

T is the temperature in K

R is the universal gas constant and is always 8.314J·K‾1

M is the mass of gas in g

Mr is the molecular mass of the gas (Air = 28.96g/mol)

Tank volume = 450 litres ( 0.45m³)

pV = (m/Mr)RT Change equation to find the mass m = (pV Mr)/RT

((280x10⁵)x0.45x28.96) / (8.314 x 282.62) = 15529g = 155.3kg

I'm pretty sure the mass of air in a 450litre air tank is not 155.3kg's but this is the only answer I keep getting so what have I missed?

A pressurised air tank supplies compressed air to a new hybrid air engine. When the hybrid engine is not running the absolute pressure in the tank is 320 bar and the temperature of the air is 50°C.

**Calculate the temperature of the air in the high pressure air tank when the air engine starts and the absolute pressure in the tank drops to 280 bar. Volume remains constant.**Using the General Gas Law: P1xV1/T1 = P2xV2/T2

Simplify the equation to P1/T1 = P2/T2 as there is no change to the volume.

Step 1) Convert the known temperature to Kelvin = T1 = 50⁰C + 273 = 323K

Insert values into the equation:

320/323 = 280/T2

T2 = (280/320) x 323 =282.62K

The temperature of the air in the high pressure air tank at 280 bar is 282.62K

**Calculate the mass of air in the pressurised air tank using the temperature and pressure from part (a) and the information given here below.**Using the Characteristic Gas Law equation pV=nRT which can also be written as pV = (m/Mr)RT)

P is the pressure in Pa

V is the volume in m³

N is the amount of gas (in moles)

T is the temperature in K

R is the universal gas constant and is always 8.314J·K‾1

M is the mass of gas in g

Mr is the molecular mass of the gas (Air = 28.96g/mol)

Tank volume = 450 litres ( 0.45m³)

pV = (m/Mr)RT Change equation to find the mass m = (pV Mr)/RT

((280x10⁵)x0.45x28.96) / (8.314 x 282.62) = 15529g = 155.3kg

I'm pretty sure the mass of air in a 450litre air tank is not 155.3kg's but this is the only answer I keep getting so what have I missed?