DF8 - Combustion of Fuels, Gas Calculations and the Ideal Gas Equation

Question 1

NOTE:

Gases occupy the SAME VOLUME of space under the same conditions.

Answer 1

NOTE:

Gases occupy the SAME VOLUME of space under the same conditions.

Question 2

How do you work out moles (using vol)?

Answer 2

moles =

volume (dm3)
____________
molar gas volume (24dm3mol-1 at rtp)

Question 3

What is meant by molar gas volume?

Answer 3

MOLAR GAS VOLUME

The volume that a mole of gas occupies.

This is measured in dm3mol-1

Question 4

What is the value for standard room temperature?

Answer 4

298K

Question 5

What is the value for standard pressure?

Answer 5

101.3kPa
or
1 atmosphere

Question 6

Worked example: CALC INVOLVING REACTING MASSES AND VOLS

What volume of CO2 is produced when 15g of CaCO3 completely decompose?
Assume that one mole of gas occupies 24cm3 at rtp.

Answer 6

Step 1: Write the equation.

CaCO3 –> CaO + CO2

Step 2: Work out the moles of the calcium carbonate and carbon dioxide from the equation.

One mole of CaCO3 decomposes to produce one mole of CO2.

Step 3:Write out the mass and volume of one mole for calcium carbonate and carbon dioxide.

molar mass CaCO3 = 100.1g

molar vol of CO2 = 24.0dm3

Step 4: Calculate volume of CO2

1g = 24/100.0

15g = 24/100.1 x 15

= 3.6dm3

Question 7

When temp or pressure are different from r.t.p what equation do you do / use?

Answer 7

pressure, P (Pa) x Volume, V (m3) =

amount of gas, n (moles)
x
gas constant, R (JK-1 mol-1)
x
temperature, T (K)
\_\_\_\_\_\_\_\_\_\_\_

PV=nRT

Basically pressure x volume = gas in mols x gas constant x temp

The gas constant R has the value 8.31 JK-1 mol-1

Question 8

Worked example: CALC VOLUME FROM IDEAL GAS EQUATION

What is the volume of 1 mole of gas at 100kPa pressure and 16 degrees C?

(Gas Constant = 8.31 JK-1 mol-1)

Answer 8

Step 1: Convert kPa to Pa

1 kPa = 1000 Pa

100 x 1000 = 100,000 or 1 x 10^5 Pa

Step 2: Convert degrees C to K by adding 273 to the degrees C value.

16 + 273 = 289 K

Step 3: Rearrange the ideal gas equation to make volume the subject and substitute in the values

V = (nRT) / P

V = (1 x 8.31 x 289) / (1 x 10^5)

V = 0.0240 m3 = 24 dm3

_______________

16 degrees C and 1 x 10^5 are the values for rtp.

Question 9

Worked example: CALC PRESSURE FROM THE IDEAL GAS EQUATION

What is the pressure if 5.0g of nitrogen is present in a volume of 50cm3 at 300K?

( Gas constant = 8.31 ; Mr N2 = 28 )

Answer 9

Step 1: Calculate the moles of nitrogen.

n = mass / ram =
n = 5.0 / 28 = 0.179 mol

Step 2: Convert cm3 to m3

1cm3 = 1 x 10^-6 m3

So to convert from cm3 to m3, multiply the cm3 value by 1 x 10^-6.

50 x 1 x 10^-6 = 5 x 10^-5 m3

Step 3: Rearrange the ideal gas equation to make pressure the subject and re-substitute in the values.

P = (nRT) / V
P = (0.179 x 8.31 x 300) / (5.0 x 10^-5)
P = 8.9 x 10^6 Pa

____________
This is about nine times atmospheric pressure.

Question 10

cm to dm to m

Answer 10

cm - /10 - dm - /10 - m

Question 11

cm2 to dm2 to m2

Answer 11

cm2 - /100 - dm3 - /100 - m2

Question 12

cm3 to dm3 to m3

Answer 12

cm3 - /1000 - dm3 - /1000 - m3