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Lindenwood Chemistry > Gen Chem Exam 4 Flashcards > Flashcards

Gen Chem Exam 4 Flashcards

1
Q

What is the oxidation state of each oxygen in O2?

A

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2
Q

What is the oxidation state of each fluorine in F2?

A

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3
Q

What is the oxidation state of each oxygen in O3?

A

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4
Q

What is the oxidation state of each hydrogen in H2?

A

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5
Q

What is the oxidation state of Fe3+ ?

A

It’s 3+, silly. :-)

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6
Q

What is the oxidation state of oxygen when it is in a compound with any other element?

A

Oxygen is always -2 oxidation state when it is bonded to a different element.

(peroxides are an exception to this rule, but I won’t ask you about them)

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7
Q

What is the oxidation state of hydrogen when it is in a compound with any other element?

A

Hydrogen is always +1 oxidation state when it is bonded to a different element.

(hydrides like NaH are an exception to this rule, but I won’t ask you about htem)

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8
Q

What is the oxidation state of fluorine when it is in a compound with any other element?

A

Fluorine is always -1 oxidation state when it is bonded to a different element.

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9
Q

How do you figure out the oxidation state of an atom which is not covered by any of the other rules?

A

The total charge of the whole compound is equal to the oxidation states of all the atoms inside it summed up. So if you are only missing the oxidation state of one atom, set up an equation to figure it out.

If you are missing multiple atoms, then you have to make a guess based on what column it is in on the periodic table.

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10
Q

What are the steps in order to balance a DIFFICULT electrochemistry (redox) reaction using the HALF REACTION METHOD?

A

1.) Split up the reaction into one where atoms are being oxidized and the other where atoms are being reduced.
2.) Balance atoms that are not oxygen or hydrogen by adding coefficients
3.) Balance oxygens with water.
4.) Balance hydrogens with H+
5.) Balance charges with electrons
6.) Recombine the two reactions in such a way that the electrons perfectly cancel out. You may need to multiply the individual reactions by something to make this happen.
7.) Simplify, and then you are done if it is in acidic or neutral solution.
8.) If it is in basic solution, add OH- to BOTH sides. The amount of OH- you need to add to each side is the same as the H+ on one side.
9.) On the side that has OH- and H+, combine those to make water. Simplify all waters, and then you are done with it in a basic solution.
10.) CHECK YOUR WORK BY COUNTING THE ATOMS AND CHARGES.

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11
Q

What are the steps to writing an EASY electrochemistry reaction
(e.g. in a problem where I’m about to ask you to solve for a voltage.)

A

1.) Write 2 half reactions where nothing is happening. Each atom turns into itself.

2.) Figure out which side to put electrons on. The anode reaction should have electrons as products, and the cathode should have them as reactants.

3.) Put the higher atom charges on the sides with electrons.

4.) Change the number of electrons in each reaction so that within a given reaction the charges balance.

5.) Combine the two half reactions into one, in such a way that the electrons perfectly match. You may need to multiply some half reactions by a constant for this to happen.

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12
Q

How do you solve for E-standard with a table of standard reduction potentials

A

1.) Pick the two rows on the table that have the right atoms and atom charges in them.

2.) Flip the sign of the voltage of the half reaction that is going to be the anode.

3.) Sum up that revised voltage with the other voltage.

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13
Q

How do you calculate the voltage of an electrochemical cell?

A

1.) Write a balanced reaction.

2.) Solve for E-standard with a table of data.

3.) Calculate Q using Products / Reactants, ignoring solids, and including exponents when needed.

4.) Use the Nernst equation

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14
Q

One side of the electrochemical cell is an anode, and the other is the cathode. Which way do electrons flow?

A

Electrons always flow from anode to cathode.

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15
Q

What does oxidation mean?

A

Oxidation is loss of electrons. It means the atom’s charge is going UP.

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16
Q

What does reduction mean?

A

Reduction is gain of electrons. It means the atom’s charge is going DOWN.

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17
Q

Where does oxidation happen? The anode or the cathode?

A

The anode.

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18
Q

Where does reduction happen? The anode or the cathode?

A

The cathode.

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19
Q

Which way do positive ions flow in the salt bridge?

A

They flow towards the cathode
( to cancel out the negative electrons that are also headed there)

20
Q

Which way do negative ions flow in the salt bridge?

A

They flow towards the anode
( to replace the electrons that just left from there)

21
Q

What is the reducing agent?

A

It is the reactant chemical that CAUSESthe OTHER chemical to get reduced.

So the reducing agent, ITSELF, is the chemical that is being oxidized

22
Q

What is the oxidizing agent

A

It is the reactant chemical that CAUSESthe OTHER chemical to get oxidized

So the oxidizing agent, ITSELF, is the chemical that is being reduced

23
Q

When you see “n” in an electrochemistry formula, what does that mean?

A

It is the number of electrons that are being transferred in the full reaction.

It is the number of electrons that “canceled out” when assembling the two half reactions.

24
Q

Which value of R do you use on this test? 8.314 J mol^-1 K^-1 or 0.08206 L atm mol^-1 K^-1

A

8.314 J mol^-1 K^-1

25
Q

How do you turn a line notation into a picture?

A

The line notation always has this format:

Anode | Anode’s solution || Cathode’s solution | Cathode

And electrons always flow through the wire from anode to cathode.

26
Q

When you multiply a reaction by a constant, what do you do to its voltage?

A

Absolutely nothing :-)

27
Q

On this test, what units should temperature be in?

A

Kelvin, of course!

The ONLY time in this class you can EVER use Celsius is in mC(delta T) on test 3 material.

28
Q

You see an activation energy in kJ/mol. What are the first few things you should do?

A

Convert it to J / mol by multiplying by 1000

Realize that this problem probably needs you to use the Arrhenius equation.

29
Q

You see three graphs of data. The x axis are all time. The three y axis are:
Molarity
Ln (Molarity)
1 / Molarity
How do you figure out the order of the reaction and its k value?

A

Only pay attention to the y axis of the graph. Find the one whose data is linear.
Molarity (0th order)
Ln (Molarity) (1st order)
1 / Molarity (2nd order)
On these sorts of graphs, the k is always the absolute value of the slope.

30
Q

When you convert a voltage into a delta G value, what units does it come out in?

A

Joules per mole.

31
Q

What does the word Rate mean?

A

Change in molarity divided by change in time.

32
Q

If you know the rate in terms of one chemical, but you want the rate in terms of a different chemical, how do you switch?

A

Use the mole to mole ratio in the balanced reaction. Divide by your current chemical’s coefficient, and multiply by your desired chemical’s coefficeint.

33
Q

You have a reaction with 3 reactants, A B and C. What is it’s blank rate law?

A

Rate = k [A]^a [B]^b [C]^c

34
Q

You have a table that lists the initial molarities of several experiments and the initial rates of the reaction for each of those experiments. How do you solve for the rate constant?

A

First write a blank rate law.

Then pick pairs of rows off the table where only one molarity is changing at a time (if possible). Fill in the rate laws with their information to solve for the orders (exponents)

Only after you have the exponents can you choose any row and plug everything in to solve for k.

35
Q

You are working with a kinetics problem where temperatures are changing. What sort of equation will you probably need?

A

The Arrhenius equation. There are 3 versions. Any of them would probably be fine.

36
Q

You are dealing with a kinetics problem that involves time. What sort of equation will you probably need?

A

You will probably need one of the 3 integrated rate laws.

(The only exception is if you are solving for a Rate, which is Change in molarity / Change in time)

37
Q

You are given a graph whose data is linear. The x axis is 1/Temperature.
The y axis is Ln(rate constant)

How do you use the equation of the line to find the activation energy?

A

Since this graph was prepared with the Arrhenius equation in mind, the slope can be multiplied by negative R to get the activation energy.

38
Q

You are given the half life of a first order reaction in a long problem. What is a good first step to do?

A

Turn the half life into the rate constant with the formula t = 0.693 / k

39
Q

When I ask you a kinetics problem involving nuclear isotopes, what is the order of the reaction?

A

I will only ask you about spontaneous nuclear reactions, so they will always be 1st order. It won’t say 1st order in the problem, though. You just have to know it.

40
Q

To prove that a given nuclear reaction is balanced, what two very simple pieces of math do you need to show?

A

The sum of the TOP numbers on the left = The sum of the TOP numbers on the right

The sum of the BOTTOM numbers on the left = The sum of the BOTTOM numbers on the right

41
Q

What are the symbols for each of the following. Include the top and bottom numbers.
1.) Alpha particle
2.) Electron
3.) Positron
4.) Neutron
5.) Gamma ray
6.) Proton

A

Symbol Top Number Bottom number
He 4 2
e 0 -1
e 0 1
n 1 0
greek letter gamma 0 0
H or p, I’ll accept either 1 1

42
Q

What is the difference between a particle being captured vs. it being emitted or produced?

A

Capture = the particle is a reactant
Emitted or Produced = the particle is a product

43
Q

How do you calculate a binding energy?

A

1.) Write a reaction where the given atom is breaking apart into all its pieces

2.) Do a “products - reactants” with the masses in that reaction. Make sure everything is in kg

3.) Turn that answer (the mass defect) into an energy with E = m c^2

4.) Divide by the number of pieces that the atom has (the number of nucleons)

5.) if the answer choices are in a different unit than J/nucleon, use stoichiometry to convert your answer to match the desired units.

44
Q

What is the “trick” to doing carbon dating style problems?

A

Use the decay rates as if they were molarities.

45
Q

In a first order kinetics problem, you are given percents in the problem. How do you go about solving this problem

A

Assume some starting amount, like “We started with 100 grams” and then multiply things by the percentages as needed.

Lindenwood Chemistry (8 decks)

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