|ll|lll|'s question thread

[|ll|lll|]

Don't think I'd have much questions for unit 4, but I would create thread anyway

Have these questions unanswered / not properly answered for a while...

1. What's the difference between a closed and open system?
2. What's an example of a thermoneutral equation? (With regards to enthalpy change) I mean, is it possible in practical situations for energy to break bonds = energy to form bonds?
3. Does a catalyst increases rate of forward and backward reactions at the same rate? If so, does this mean that if a catalyst doubles the speed of forward reaction, so essentially, it'd take half the time for system to be at equilibrium?

[SenriAkane]

1.
closed system: No external energy or chemical is added to or removed from the system in a chemical reaction
open system: A system where energy or chemicals is added to a particular system.

3.A catalyst increases rate of both forward and backward reactions at the same rate. Hence the statement it takes half the time for the system to reach equilibrium is indeed true. 

[Graphite]

2. Enthalpies for the formation of elements (H2, Br2, Cl2)

[t35t]

1.
closed system: No external energy or chemical is added to or removed from the system in a chemical reaction
open system: A system where energy or chemicals is added to a particular system.

3.A catalyst increases rate of both forward and backward reactions at the same rate. Hence the statement it takes half the time for the system to reach equilibrium is indeed true.

for 1. Would a closed system therefore result in dynamic equilibrium?

[thushan]

1.
closed system: No external energy or chemical is added to or removed from the system in a chemical reaction
open system: A system where energy or chemicals is added to a particular system.

3.A catalyst increases rate of both forward and backward reactions at the same rate. Hence the statement it takes half the time for the system to reach equilibrium is indeed true. 

a closed system can exchange energy but not matter - it's an isolated system that cannot exchange either.

[t35t]

I came across a question about a plastic bag- the reaction was the evaporation and re-formation of H2O in this "closed" and "open" bag. Is this essentially the same thing as a closed and open system?

[Graphite]

Are you asking if that is a good analogy to visualise an open and closed system?
I think it is not too important as to whether it is precisely an open or closed system but rather logically, if the chemicals are locked in a closed object, the vapour builds up and the vapour pressure is establised as more vapour leaves the surface of the liquid and at the same time vapour re enters the liquid until both processes occur at the same rate.
In contrast, if the object is opened, the vapour escapes continually, with very minimal vapour returning back to its liquid state. The vapour pressure would never be established.

[Graphite]

Because when you form a pure element, it must be derived from itself. There would be no change and thus the enthalpy difference is 0.