VCE Chemistry Question Thread

[pha0015]

You can’t determine that just with a graph. However you can if you know what caused the shift in the concentration time graph. For example, consider the reaction A + B —> C. The question says temperature was increased and you notice on the graph that the concentration of C also increased. You can deduce from this that the reaction is endothermic as an increase in temperature increases the yield.

Thanks. That's exactly what I was looking for, although the question did ask us to infer what the change was by ourselves so that's why I didn't include it in my question.

[hums_student]

Hey guys, does anyone have any good resources they're willing to share for writing up the practical investigation in unit 4? Especially if anyone have a sample prac report they did when they were doing chem? I don't really mind if it's a low scoring one, I have no idea where to start and am willing to take anything!

Thanks guys!

[PopcornTime]

What does it mean by an excited atom and how is this represented with an electron figuration (subshell notion)?

Whats the difference between ground state electron configuration and excited electron configuration?

What is emission spectra?

Why is the major force in PCl3 and OF2 dipole-dipole?

[sweetcheeks]

What does it mean by an excited atom and how is this represented with an electron figuration (subshell notion)?

Whats the difference between ground state electron configuration and excited electron configuration?

What is emission spectra?

Why is the major force in PCl3 and OF2 dipole-dipole?

Have a go at these questions first yourself. It's always better to attempt to answer them before someone just gives you an answer.

[IonianDeo]

Which one of the following changes would decrease the rate of the reaction
between zinc metal and dilute hydrochloric acid?
A Increasing the temperature of the hydrochloric acid
B Decreasing the size of the pieces of zinc
C Decreasing the concentration of the hydrochloric acid
D Decreasing the volume of hydrochloric acid used

Heinemann Chemistry 2 5th Edition
7.1 Rates

Text says answer is C but why can't it also be D?

[sweetcheeks]

Which one of the following changes would decrease the rate of the reaction
between zinc metal and dilute hydrochloric acid?
A Increasing the temperature of the hydrochloric acid
B Decreasing the size of the pieces of zinc
C Decreasing the concentration of the hydrochloric acid
D Decreasing the volume of hydrochloric acid used

Heinemann Chemistry 2 5th Edition
7.1 Rates

Text says answer is C but why can't it also be D?

Rate of reaction is dependent upon the concentration of species. Although decreasing the volume of HCl used will decrease the amount of HCl present, the concentration is still the same.

[A TART]

For this question, wouldn't the reaction be an exothermic reaction? An increase in temperature has resulted in a decrease in the  concentration of products and increase in reactants (indicating a backward reaction response from  the system). Wouldn't this indicate an exothermic reaction? The answer says it's endothermic.

https://i.imgur.com/axaKV67.png
https://i.imgur.com/5fduQGC.png

[Lear]

It is asking you for the thermochemical nature of the REVERSE reaction. Your logic is spot on other than that. The forward reaction is indeed exothermic.

[Guideme]

Can anyone help me with this question pls ?

I remember my teacher talking about NaoH bonding with the most strongest base or something, but i still dont understand.

Thank you

[TheBigC]

Can anyone help me with this question pls ?

I remember my teacher talking about NaoH bonding with the most strongest base or something, but i still dont understand.

Thank you

Hey there, when NaOH is added, the base dissociates almost entirely. This results in an increase in the concentration of OH- ions. Thus, if we examine the reaction quotient or concentration fraction, Qc, we will find that Qc > Kc. This ultimately produces a net backward reaction. Given such, we can rule out B and D. This leaves us with A and C. C is incorrect as the addition of a base increases pH (as OH- ions enter the solution). Hence, the answer is A.

[meymanic]

Hey guys I had a question, what will a reaction rate Vs time graph look like when reactants is removed and hence reverse reaction is favoured?

[A TART]

Hi, I have a quick question.

For equilibrium questions with "explain", do I have to mention Le Chatelier's principles to receive a mark, or is simply explaining it sufficient?

ie: The system partially opposes this change by favouring the reaction that produces more particles, hence a forward reaction is favoured.

or do I have to say : "according to Le Chatelier's principle...."?

[TheBigC]

Hey guys I had a question, what will a reaction rate Vs time graph look like when reactants is removed and hence reverse reaction is favoured?

I could tell you the answer to this question, but that wouldn't serve to aid you in your endeavours. I recommend that you take an equilibrium system, such as one consisting of ammonia, hydrogen gas and nitrogen gas and question what might occur if hydrogen gas were removed. Ask yourself:

- How has the concentration fraction or reaction quotient (Qc) changed?
- Is Qc > or < Kc?
- How could the system partially oppose this change?
- On what 'side' of the reaction are a greater frequency of collisions now occurring? Hence, in reference to dynamic equilibrium, which direction (forward or reverse) has the greater rate of reaction?

[TheBigC]

Hi, I have a quick question.

For equilibrium questions with "explain", do I have to mention Le Chatelier's principles to receive a mark, or is simply explaining it sufficient?

ie: The system partially opposes this change by favouring the reaction that produces more particles, hence a forward reaction is favoured.

or do I have to say : "according to Le Chatelier's principle...."?

You should be fine either way.

[teddiee]

I was wondering could someone give some info on how the shape of a molecule impacts intermolecular forces and physical properties like solubility, viscosity and/or surface tension?