AQA Chemistry Unit 2 with Anon_98.

So I recently made a similar thread for Biology bc I thought it'd help with the particular circumstance but it surprisingly turned out to be a whole lot more useful than I thought it would be + a really efficient way for me to learn too.

As a result, I think this will be my new way of revising for stuff bc not only does it enable me to access all the info within a single thread which is v convenient, but it seems to also help other people which I suppose is a bonus.

Anyway, I've done most of this unit and only have a few topics left but I'm going to start from the very beginning bc ..well, extra practice- why not?

Then hopefully it'll mean I can completely focus on something new tomorrow rather than drag it out for 3 days.

I find it really hard to motivate myself atm + so my aim is that if I can just post at least one sub-topic/something on here at least, every 2hrs everyday until my exams are over then it'll hopefully benefit me bc it means I'm doing something.

..And something is always better than nothing. :h:

Reply 1

Kevin De Bruyne

21

Original post by Anon_98

So I recently made a similar thread for Biology bc I thought it'd help with the particular circumstance but it surprisingly turned out to be a whole lot more useful than I thought it would be + a really efficient way for me to learn too.

As a result, I think this will be my new way of revising for stuff bc not only does it enable me to access all the info within a single thread which is v convenient, but it seems to also help other people which I suppose is a bonus.

Anyway, I've done most of this unit and only have a few topics left but I'm going to start from the very beginning bc ..well, extra practice- why not?

Then hopefully it'll mean I can completely focus on something new tomorrow rather than drag it out for 3 days.

I find it really hard to motivate myself atm + so my aim is that if I can just post at least one sub-topic/something on here at least, every 2hrs everyday until my exams are over then it'll hopefully benefit me bc it means I'm doing something.

..And something is always better than nothing. :h:

Subscribing once more.. maybe a nap after all this time might be a bit useful before you get down to the real work :tongue:

Spoiler

(edited 7 years ago)

Reply 2

Anon_98

OP

19

Original post by SeanFM

Subscribing once more.. maybe a nap after all this time might be a bit useful before you get down to the real work :tongue:

Spoiler

ty!

+

I cba to nap. :woo:

Reply 3

username2230787

15

Anon you are so great :hugs:

I know absolutely nothing about chemistry but it sounds hard so goodluck :lovehug:

I really admired your determination in the other thread and im sure biology went better than you think <3
love you Anon and goodluck, will be over soon :woo:

x

Reply 4

Anon_98

OP

19

Original post by Salamandastron

Anon you are so great :hugs:

I know absolutely nothing about chemistry but it sounds hard so goodluck :lovehug:

I really admired your determination in the other thread and im sure biology went better than you think <3
love you Anon and goodluck, will be over soon :woo:

x

Ty lots, I v much hope your exam went well today <3

Reply 5

Anon_98

OP

19

Energetics - Enthalpy Change - Topic 1.

- know that reactions can be endothermic or exothermic

- understand that enthalpy change (DH) is the heat energy change measured under conditions of constant pressure

-know that standard enthalpy changes refer to standard conditions, i.e. 100 kPa and a stated temperature (e.g. DH298

- be able to recall the definition of standard enthalpies of combustion (DHc ) and formation (DHf)

Exothermic

- Energy released to the surroundings.
- Temperature rises.

Endothermic

- Energy absorbed from the surroundings.
- Temperature falls.

Enthalpy change. (DH) - The heat energy change of a chemical reaction measure under conditions of constant pressure.

DH = Enthalpy of products - Enthaply of reactants.

Standard conditions are:

- Pressure of 100KPa
- A stated temperature. (E.g. 298K)

The standard state of an element is the state it is found in under standard conditions.

E.g. Sodium - Na(s)
Chlorine - Cl2(g)
Oxygen - O2(g)
Water - H2O(l)

Standard enthalpy of formation. - The enthalpy change 1 mol of a compound is formed from it's elements under standard conditions, all reactants and products being in their standard states.

Standard enthalpy of combustion. - The enthalpy change when 1 mol of a substance is completely burned in oxygen under standard conditions, all reactants and products being in their standard states.

Reply 6

Anon_98

OP

19

+ these are the Endo/Exo graphs.

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Reply 7

Anon_98

OP

19

Energetics - Calorimetry - Topic 1.

be able to calculate the enthalpy change from the heat change in a reaction using the equation q = mcDT

Energy transferred to or from water =

Mass of water x Specific heat capacity x Temperature change of water.
q = mcDT

Reply 8

Anon_98

OP

19

Energetics - Simple application of Hess' Law. - Topic 1.

know Hess’s Law and be able to use it to perform simple calculations, for example calculating enthalpy changes for reactions from enthalpies of combustion or enthalpies of formation

Hess' Law. - If a change can be brought about in more than one way then the overall enthalpy change is independent of the route taken.

(In a diagram, the opposite way to the arrow is always a minus)

Reply 9

Anon_98

OP

19

The cycle thingy.

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Reply 10

Anon_98

OP

19

Energetics - Bond enthalpies. - Topic 1.

- be able to determine mean bond enthalpies from given data

- be able to use mean bond enthalpies to calculate a value of DH for simple reactions

DHr = ΣDHf (products) - ΣDHf (reactants)

Standard enthalpy of formation.

DHf = products - reactants.

~

DHr = ΣDHc (reactants) - ΣDHc (products)

Standard enthalpy of combustion.

DHc = reactants - products.

~

Bond enthalpy - The energy needed to break 1 mol of a particular covalent bond in the gaseous state averaged over several compounds where the bonds exists.

Bond breaking is an endothermic process, Bond forming is an exothermic process.

Bond enthaply formula.

DHr = Σ (enthaply bonds broken) - Σ (enthalpy bonds formed)

Reply 11

Anon_98

OP

19

Kinetics- Collision theory - Topic 2.

-understand that reactions can only occur when collisions take place between particles having sufficient energy.

- be able to define the term activation energy and understand its significance

- understand that most collisions do not lead to reaction

- Molecules collide elastically and transfer energy.
- Many collisions do not result in a reaction.

Activation energy - Minimum energy needed for a reaction to occur upon collision of particles.

Reply 12

Anon_98

OP

19

Kinetics- Maxwell-Boltzmann distribution - Topic 2.

- have a qualitative understanding of the Maxwell–Boltzmann distribution of molecular energies in gases

- be able to draw and interpret distribution curves for different temperatures

The graph is basically the number of particles against energy.

Curve at higher temperature.

- Shifts to the right.
- Area under the curve remains the same.
- Peak is lower.

Reply 13

Anon_98

OP

19

+ this is what it looks like:

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Reply 14

username1539513

21

Subscribing to this thread

Reply 15

Anon_98

OP

19

Kinetics- Effect of temperature/concentration on reaction rate + Catalysts - Topic 2.

- understand the qualitative effect of temperature changes on the rate of reaction
- understand how small temperature increases can lead to a large increase in rate
- understand the qualitative effect of changes in concentration on rate of reaction
- know the meaning of the term catalyst
- understand that catalysts work by providing an alternative reaction route of lower activation energy

Rate of reaction. - Change in concentration of reactant per unit time.

Effect of an increased concentration (or pressure if gas)

- Number of particles in a given volume increases.
- Increased frequency of collision.

Effect of smaller size particles.

- Surface area increases.
- Increased frequency of collision.

Effect of an increase in temperature.

- Small temperature rise leads to large increase in rate.
- Energy of particles increases.
- Many more molecules have the activation energy or greater.
- Many more successful collisions in a given time.

Catalyst. - speeds up a reaction without being used up.

The way it works is that:

- It provides an alternative reaction route of lower than the activation energy.
- More particles have activation energy.

(edited 7 years ago)

Reply 16

Anon_98

OP

19

Equilibria -The Dynamic nature of Equilibria - Topic 3.

- know that many chemical reactions are reversible
- understand that for a reaction in equilibrium, although the concentrations of reactants and products remain constant, both forward and reverse reactions are still proceeding at equal rates

Dynamic

- Both forward and backward reactions are proceeding at equal rates.
- Concentrations of reactants and products remain constant.

Reply 17

Anon_98

OP

19

Equilibria - Effects of changes of pressure, temp + conc on a system in equilibrium - Topic 3.

- be able to use Le Chatelier’s principle to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions
-know that a catalyst does not affect the position of equilibrium

Homogeneous- Both reactants and products are in the same state.

Le Chatelier's principle - A system in equilibrium will respond to oppose any change imposed upon it and shift the equilibrium position.

~

Change in temperature.

An increase in temperature moves the equilibrium position to the endothermic side of the equation to oppose the change.

Change in pressure.

An increase in pressure moves the equilibrium position to the side of the equation with fewer moles of gas to oppose the change.

Change in concentration.

An increase in concentration of a reactant shifts the equilibrium position to the right hand side to oppose the change.

Addition of a catalyst.

Increases the rate at which equilibrium is attained, but does not change the position of equilibrium.

Once equilibrium is attained, addition of catalyst both increases rate of both forward + backward reactions equally.

Reply 18

troubadour.

19

Subbing.

You go, Anon! :rave:

Spoiler

Reply 19

metrize

18

New spec or old spec?

AQA Chemistry Unit 2 with Anon_98.

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