Unit 14 D2 HELP! BTEC LEVEL 3 SCIENCEWatch
Let me make this easy peasy lemon squeezy for you (sorry but you are probs a baby compared to some of us haha )
Pressure affects the volume of a gas. Boyles Law states that the volume of a gas is inversely proportional to the pressure exerted on it at constant temperature (why is constant temp a condition?? - yes, well done! - cos temp also has an effect on volume of gas [remember Charles' Law?)
So, it is conceivable that if you press a gas like (sort of by increasing pressure), you can imagine the volume will reduce - like compressing a flexible piece of rubber (just to explain) - the harder you press a soft elastic ball (e.g.) the smaller it will become, agreed?
Ok, now let us take chemical reactions:-
e.g. to make ammonia (Haber process?? - sorry I did my A level chemistry 15 years ago - now you can guess how much (actually how little!) hair I have on my head ), you react hydrogen with nitrogen.
3H2 + N2 ---> 2NH3
By Avogadro's rule, there are 4 moles (therefore 4 volumes) of gas on left of equation [3 + 1] and 2 volumes on right - yeah?
so from left to right, we are reducing total volume of gas - makes sense? OK good! So you can imagine Going back to Boyles Law above, that because higher pressure makes volume smaller (remember like compression?), so higher pressure will drive this equation to the right i.e. more ammonia gas (NH3) [less volume = 2 moles] will be produced rather than reversed equation (breakdown of ammonia into N2 and H2)[more volume = 4 moles].
Conversely (= other way round) In a reaction where volume increases to the right, you will need to use low pressure to drive the equation.
I hope this helps.
M (Specialist biology tutor)