Further gas equations

Previously in gas equations we learnt that - n=V/24000. There is one other side to this equation for when those hateful questions come up! As always we will run through this simply and easily but first we need to start off with the symbols that make up this equation:

n = as always is mol
T = Temperature measured in K
P = Pressure measured in KPa
V = Gas volume measured in dm cubed
R = The gas constant

Now I understand that this may seem like a lot of info but let break this down:

STP means the standard temperature and pressure which results in-
- Standard temperature being 298K
- Standard pressure being 100KPa

As usual we don't question and in the legendry words of the Beatles 'Let it be' ... I should probably stop with the jokes! The other thing that is quite important that you know is the gas constant which is 8.314mol^-1K^-1 and once again keep the previous sentence in mind!

The actual equation for this is:

PV = R x nT
or
Pressure x gas volume = mol x Temperature x The gas constant
Even simpler:
100 x gas volume= mol x 298 x 8.314

The last part of this is made by merely substituting in what we have learnt about the figures of specific parts of the equation. Lets try it!

How many tonnes of lead could be made in a furnace when there are 50 tonnes of lead oxide mixed with carbon? Lets do the balanced equation first:

2PbO + C ----> 2Pb + CO₂

The ratio of lead to lead oxide is equal as 2:2 so using our amount of substance equation we can find out the mol of lead:

Pb = 207.2
O = 16
PbO = 223.2

50/223.2 = 0.224 (3 sig figs)
sig figs - significant figures

This ratio means we get to keep the mol the same for both sides of the equation and dependent upon the equations ratio it can alter the ratio. For example:

1:2 So for every one lot of a substance there are two lots of the opposing substance so the mol must be timesed by two.

Here we can use this to find out how many tonnes of lead in the products was created. So here's what we do:

Step 1: we take the mol from the previous equation and then figure out the molar mass of lead alone
Step 2: Look at the periodic table to find out that said mass is 207.2
Final step: Times the mol and times them by the molar mass of lead resulting in 46.4 tonnes of lead.

Did you find this helpful? Feel free to drop a comment and let me know what you liked and if I have missed something!

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A level Chemistry

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