Q&A - P4 Science

[ttyh]

Jar x & y volume - 1000cm3 each.

200cm3 of air was first pumped into each jar.
Additional air was pumped into each jar as below
jar x - additional 600cm3, jar y - additional 900cm3
What is the final volume of air in each jar?

[tianzhu]

ttyh:

Jar x & y volume - 1000cm3 each.

200cm3 of air was first pumped into each jar.
Additional air was pumped into each jar as below
jar x - additional 600cm3, jar y - additional 900cm3
What is the final volume of air in each jar?

Hi

1000cm3 each

Air has no definite volume and can be compressed.

Best wishes

[ttyh]

tianzhu:

ttyh:

Jar x & y volume - 1000cm3 each.

200cm3 of air was first pumped into each jar.
Additional air was pumped into each jar as below
jar x - additional 600cm3, jar y - additional 900cm3
What is the final volume of air in each jar?

Hi

1000cm3 each

Air has no definite volume and can be compressed.

Best wishes

One of the gas law defines P1V1=P2V2
surely the volume of air in jar will change?

[mother777]

ttyh:

tianzhu:

[quote=\"ttyh\"]Jar x & y volume - 1000cm3 each.

200cm3 of air was first pumped into each jar.
Additional air was pumped into each jar as below
jar x - additional 600cm3, jar y - additional 900cm3
What is the final volume of air in each jar?

Hi

1000cm3 each

Air has no definite volume and can be compressed.

Best wishes

One of the gas law defines P1V1=P2V2
surely the volume of air in jar will change? [/quote]As tianzhu already highlighted, air has no definite volume and can be compressed.

In another words air takes the shape of container (box/bottle/jar etc) in which it is pumped in.

If the volume of air pumped inside is less than the volume of jar (volume of jar is fixed by its shape and will not change), it will just expand to the volume of jar. The pressue of the air will just change..

And if the volume of the air pumped inside is more than the volume of jar, then air will get compressed (increase in pressure) to fit inside the smaller volume of jar.

To summarize, the volume of jar is const..hence volume of air will also follow it..

Hope this helps to understand the question..

[atutor2001]

ttyh:

tianzhu:

[quote=\"ttyh\"]Jar x & y volume - 1000cm3 each.

200cm3 of air was first pumped into each jar.
Additional air was pumped into each jar as below
jar x - additional 600cm3, jar y - additional 900cm3
What is the final volume of air in each jar?

Hi

1000cm3 each

Air has no definite volume and can be compressed.

Best wishes

One of the gas law defines P1V1=P2V2
surely the volume of air in jar will change? [/quote]Yes P1V1 =P2V2.
So both P or V may change.
However, in this case, it is only the pressure that changed, not the volume since the volume of both containers are the same.

In another word, the pressure inside container Y (the one with more mass of gas) will be higher than the pressure inside container X.

[ttyh]

I understand gases will take up the shape of the container and can be compressed.

But I still cannot understand this. Based on answers given above;
- if I pumped 1cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still at 1000cm3
- If I pumped 1,000,000cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still 1000cm3?

if we are standing at persepective of a commercial ‘Air’ seller, this doesnt make sense, isn’t it?

[Nebbermind]

ttyh:

I understand gases will take up the shape of the container and can be compressed.

But I still cannot understand this. Based on answers given above;
- if I pumped 1cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still at 1000cm3
- If I pumped 1,000,000cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still 1000cm3?

if we are standing at persepective of a commercial 'Air' seller, this doesnt make sense, isn't it?

think commercial air/gas seller sells by the kg if I'm not wrong.

[atutor2001]

ttyh:

I understand gases will take up the shape of the container and can be compressed.

But I still cannot understand this. Based on answers given above;
- if I pumped 1cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still at 1000cm3
- If I pumped 1,000,000cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still 1000cm3?

if we are standing at persepective of a commercial 'Air' seller, this doesnt make sense, isn't it?

Nebbermind is correct. Commercial \"air\" are sold by weight.

When 1cm3 of air is put into a 1000cm3 capacity container, the weight of the air inside is much lesser than the weight of 1,000,000cm3 of air. (please note that the volumes of 1cm3 of air and the 1,000,000 cm3 of air must be measured under the same pressure)

At the same time, the pressure inside the first container is much lesser than the pressure inside the second one.

If we keep pumping more and more air into the second container, the pressure inside will become more and more. At the same time, the total weight of the air inside will also become more and more. Finally, if the container is not strong enough, it will explode.

[ttyh]

As a matter of fact, I am a commercial air seller and in this industry, air is sold in m3.....

In Gas, P/V/T and Z(Compressibility) are always in relationship.
I know that P4 Science doesnt consider P/V/T and Z.

1m3 of air when pumped into a 1000m3 flask will take up the volume of the flask, because air can be expanded and compressed. But that doesnt mean the vol of air is 1000m3.
But perhaps the way the question is asked \"...what the volume of air in the flask...\" should be rephrase.
Having selling gas for a decade, Iit is hard for me to explain to my kid this way.....

atutor2001:

ttyh:

I understand gases will take up the shape of the container and can be compressed.
But I still cannot understand this. Based on answers given above;
- if I pumped 1cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still at 1000cm3
- If I pumped 1,000,000cm3 of air into a 1000cm3 capacity container, the volume of air in the container is still 1000cm3?

if we are standing at persepective of a commercial 'Air' seller, this doesnt make sense, isn't it?

Nebbermind is correct. Commercial \"air\" are sold by weight.

When 1cm3 of air is put into a 1000cm3 capacity container, the weight of the air inside is much lesser than the weight of 1,000,000cm3 of air. (please note that the volumes of 1cm3 of air and the 1,000,000 cm3 of air must be measured under the same pressure)

At the same time, the pressure inside the first container is much lesser than the pressure inside the second one.

If we keep pumping more and more air into the second container, the pressure inside will become more and more. At the same time, the total weight of the air inside will also become more and more. Finally, if the container is not strong enough, it will explode.

[atutor2001]

ttyh:

As a matter of fact, I am a commercial air seller and in this industry, air is sold in m3.....

In Gas, P/V/T and Z(Compressibility) are always in relationship.
I know that P4 Science doesnt consider P/V/T and Z.

1m3 of air when pumped into a 1000m3 flask will take up the volume of the flask, because air can be expanded and compressed. But that doesnt mean the vol of air is 1000m3.
But perhaps the way the question is asked \"...what the volume of air in the flask...\" should be rephrase.
Having selling gas for a decade, Iit is hard for me to explain to my kid this way.....

Great that you are in this industry. We can then discuss with more technical terms.

PV = nRT
where n is the number of mole of air, P is the pressure, V is the volume, T is the temperature and R is a constant.

If the number of mole of air (i.e. the amount of air by mass) is the same, then
P1V1=P2V2=nRT is a constant.
This means for the same amount (by mass) of air, when the pressure increases, the volume will decrease and vice versa.

If container X and Y are of the same volume but there are more air (by mass i.e. the number of mole, n is bigger) in container Y than container X, then

PxV=nx(RT) is not equal to PyV=ny(RT)
PxV=nx(RT) will be less than PyV=ny(RT) (because nx is less than ny)

This means that PxV < PyV. Therefore, Px<Py i.e. the pressure inside container X is less than the pressure inside container Y.

The volume of gas is not fixed. It depends on the pressure and the temperature. In Primary school, I think they need to know this concept. That is, for a given volume of gas (at a given temperature and pressure), it can be pumped into a container of different size and the new volume of the gas is the volume of the container.

Incidentally, when \"air\" is sold commercially by volume, the volume must be based on a standard (fixed) pressure and temperature. Otherwise the consumer cannot compare the actual amount of \"air\" that is being sold.