[abhishekmeena]

calculate the work done when 56g of iron reacts with with HCl in a) a closed vessel of fixed volume b) an open beaker at 300K

here in solution, answer of a) is given as 0 and in description it is written that volume of vessel is fixed.. therefore change in volume is 0... therefore PΔV = 0..  BUT HOW.... VOLUME IS FIXED i.e how volume doesnt change when iron reacts since hygroden is produced and it will occupy volume of container and that is certainly greater than volume of iron...how constant?

also plzz explain second part...
in b) vol. of solid is 0...how??? how vol. of solid is 0..

[Borek]

here in solution, answer of a) is given as 0 and in description it is written that volume of vessel is fixed.. therefore change in volume is 0... therefore PΔV = 0..  BUT HOW.... VOLUME IS FIXED i.e how volume doesnt change when iron reacts since hygroden is produced and it will occupy volume of container and that is certainly greater than volume of iron...how constant?

The volume doesn't change, as it is fixed - but pressure will go up. That means a fixed volume system after reaction went to completion has more energy (which is stored in a compressed gas).

in b) vol. of solid is 0...how??? how vol. of solid is 0..

Assuming you put solid iron in a solution, and reaction went to completion, volume of solid iron after reaction is zero. But I am just guessing what you are asking about as your question is cryptic, please elaborate.

[abhishekmeena]

http://www.mediafire.com/view/?dqd1yv2rdg5c1#n5a1h3xgl5j331q

plzz explain now..

[Borek]

If I understand it correctly, technically initial volume (that of a solid iron) is not zero, but about 7 mL - negligible when compared with the volume of gas produced (24.6 L at 27 °C).

[abhishekmeena]

yaa.....thanks...thanks for explaination..

[abhishekmeena]

but i still didnt get the a) part... since hydrogen will occupy whole vol. of beaker which is obviously changing volume.....why ΔV = 0...

[abhishekmeena]

also how you got 7ml as density is not given....

[Dan]

If the vessel is sealed and cannot expand, then volume is constant. If a gas is produced in a sealed vessel, the pressure increases. Imagine shaking a closed bottle of fizzy drink, CO₂ is being released but the bottle cannot expand (much). The pressure increase is the reason for the contents spraying out when you unscrew the lid.


Also: Could you please avoid text speak, this is a forum rule.

[Borek]

but i still didnt get the a) part... since hydrogen will occupy whole vol. of beaker which is obviously changing volume.....why ΔV = 0...

How is a beaker changing volume? It is not a rubber balloon, it is a rigid container. Imagine the reaction taking place in a steel tank - does it expand?

also how you got 7ml as density is not given....

I was brave enough to check the density somewhere else. But exact number doesn't matter much - you should know iron is a metal, and metals have - in most cases - density of at least 5 g/mL. That means its volume is in mL range, while the gas produced occupies many liters.

[abhishekmeena]

what i mean to say is that beaker is not expanding ( i am not a child)... but suppose you have 5 L of beaker in which 56g of iron reacts and hydrogen produced will ocuppy 5 L when it is sealed....so initially volume of iron was negligible but this 5L is not...so how ΔV = 0 //

[Borek]

Initially you have 5 L of hydrogen at p=0, in the end you have 5 L of hydrogen at some other pressure. ΔV is 0. ΔP is not, but work was not done.

[curiouscat]

what i mean to say is that beaker is not expanding ( i am not a child)... but suppose you have 5 L of beaker in which 56g of iron reacts and hydrogen produced will ocuppy 5 L when it is sealed....so initially volume of iron was negligible but this 5L is not...so how ΔV = 0 //

Would it be so hard to capitalize? You'll have a better shot at people helping you out if you take some effort to adhere to protocol.