CHEMISTRY COMMUNITY

Diana Andrade_4F

Yes, they're always positive!

Diana Andrade_4F

The units of t depend on the problem, but be consistent when doing calculations!

Diana Andrade_4F

We will be able to use our notes, textbook, and chemistry community! Exam should be short, but he said he'd give us 3-4 hours to complete it. He will give us more info on Saturday!

Diana Andrade_4F

Lavelle will let us know more on Saturday, look out for his emails!

Diana Andrade_4F

Final will be up on Sunday, and it is timed (3-4 hours). Lavelle will let us know more info Saturday!

Diana Andrade_4F

Photosynthesis is not spontaneous and needs an input of energy in order for it to occur. So that's why the answer is ΔG<0

Diana Andrade_4F

For some elements there will be a trend you should follow (look up a periodic table with these trends on google!), and for the unknown you can solve for. The oxidation numbers should add up to the total charge at the end.

Diana Andrade_4F

We will most likely get our test grades during discussion of week 10!

Diana Andrade_4F

You can use whichever you want to use!

Diana Andrade_4F

We will most likely get our test grades next week during discussion section

Diana Andrade_4F

Since they ultimately have the same function, I believe that one isn't more efficient than the other

Diana Andrade_4F

use Pt(s) when there's no metal conductor

Diana Andrade_4F

Yes! It's best to keep oxidized molecules to the left and reduced molecules to the right, this is also stated in the textbook.

Diana Andrade_4F

Test 2 will cover the rest of outline 4 (what wasn't on the midterm) and Outline 5 only. No kinetics!

Diana Andrade_4F

You have to look at Mn only, and we see that it goes from 7+ to 2+, thus being reduced

Diana Andrade_4F

Adding an inert gas doesn’t affect the equilibrium constant

Diana Andrade_4F

Yes, ALWAYS! Thats because there is no heat transfer.

Diana Andrade_4F

E will be positive if reaction is spontaneous!

Diana Andrade_4F

Reduction means gain of electron, it becomes more negative. While oxidation is the loss of electron, becomes more positive.

Diana Andrade_4F

Test 2 was moved to week 9 so we could have more time with the material! Also, it will include material after the midterm (outlines 4 and 5). It won't include kinetics.

Diana Andrade_4F

Definitely Gibbs Free energy (delta G)! If delta G is negative then the reaction is spontaneous, but if it’s positive it is not.

Diana Andrade_4F

To find W, you can use the equation W=(P)^a
Where “P” is the number of possible positions and “a” is the number of atoms

Diana Andrade_4F

Oh sure thing!

The pH of a 0.010 M solution of hydrofluoric acid is 2.63. What are Ka and percent ionization?

Diana Andrade_4F

Can someone explain to me how to solve problem 6 from test 1? Thank you!

Diana Andrade_4F

How do you find pOH when only given pKb?

Diana Andrade_4F

Gasses have higher entropy, while solids and liquids have their molecules tightly packed. Gas molecules can be in any location, since they are not tightly packed, which is why they "occupy more space"

Diana Andrade_4F

A closed system is when a system can only transfer energy (like heat) with its surroundings, meanwhile an isolated system can't transfer anything with its surroundings.

Diana Andrade_4F

A reaction in a bomb calorimeter is considered an isolated system because the calorimeter is closed and isolated. This means that no energy and no matter is being transferred.

Diana Andrade_4F

A closed system is when a system can only exchange energy (like heat) with its surroundings. Meanwhile, an isolated system is a system that can't exchange anything with its surroundings.

Diana Andrade_4F

Can someone explain to me how the grading works for this class, I'm a bit confused. Thanks!

Diana Andrade_4F

Adiabatic means that there is no heat transfer

Diana Andrade_4F

Yeah you are right. Positive q means reaction is endothermic since the system gained heat. Negative q means reaction is exothermic since heat is released.

Diana Andrade_4F

You can use either unit, but make sure you use the same units throughout the problem.

Diana Andrade_4F

Qv is when there's constant volume while Qp is constant pressure

Diana Andrade_4F

Why is it that when delta V = 0, delta U = q?

Diana Andrade_4F

Yeah, if a reaction is exothermic then temp will decrease. This is because the reaction is releasing heat (delta H is negative).

Diana Andrade_4F

will there be study guides for the midterm and final?

Diana Andrade_4F

You use Kc when you are given a concentration, while Kp is used when given partial pressures. However, you can use Kp to find Kc if needed.

Diana Andrade_4F

Yes, you should be able to determine if the reaction is exothermic or endothermic when given delta H.

Diana Andrade_4F

What is the difference between pKa/pKb and Ka/Kb?

Diana Andrade_4F

Each gas in a reaction has a partial pressure that all come together to make a whole pressure.

Diana Andrade_4F

In an endothermic reaction, heat is a reactant. So, if temperature increases, reactants increases so it shifts to the right and favors Products. In an exothermic reaction, heat is a product. If temperature is increased, products increase, so it shifts to the left and Reactants are favored.

Diana Andrade_4F

Why doesn't pH have units?

Diana Andrade_4F

How do you know when to use Kc or Kp when dealing with gasses? For example, in problem 5I.17 we use Kc instead of Kp, why?

Diana Andrade_4F

Autoprotolysis is when two identical molecules transfer protons.

Diana Andrade_4F

if K < 10^-3, then there are more reactants at equilibrium; this means that the equilibrium sits to the left.
if K > 10^3, then there are products at equilibrium; so equilibrium sits ti the right.
if K=1, the concentration of products and reactants are equal, so they have same stabilities.

Diana Andrade_4F

K is an equilibrium constant, while Q is a reaction quotient. K is found when the reaction is at equilibrium, but Q can be calculated at any time during the reaction. You can compare the reaction quotient, Q, to the equilibrium constant, K, to determine the direction of the reaction.

Diana Andrade_4F

K is just a ratio of products/reactants, so there are no units. Also, when calculating K, the units just cancel out.

Diana Andrade_4F

Yes, you don't include solids and liquids, only whatever is in gaseous/aqueous states when calculating Q.

Diana Andrade_4F

For this part of the problem, why do we get the square root of 41?

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