Kinetics, Equilibria and Redox Reactions

Question 1

What is oxidation?

Answer 1

Oxidation is the loss of electrons

Question 2

What is reduction?

Answer 2

Reduction is the gain of electrons

Question 3

What is a redox reaction?

Answer 3

A redox reaction is when reduction and oxidation occur simultaneously

Question 4

What is an oxidizing agent?

Answer 4

An oxidizing agent accepts electrons and gets reduced

Question 5

What is a reducing agent?

Answer 5

A reducing agent donates electrons and gets oxidized

Question 6

What oxidation states do elemental molecules and elemental atoms have?

Answer 6

0

Question 7

What is the oxidation state of a simple monatomic atom?

Answer 7

It is usually the same as its charge

Question 8

What is the oxidation state in an ion?

Answer 8

The overall oxidation state is just the ion charge

Question 9

What is the sum of oxidation states for a neutral compound?

Answer 9

0

Question 10

When is oxygen not -2 oxidation state?

Answer 10

when it is in a peroxide in which it is -1
when it is in a fluoride in which it is +2 or +1

Question 11

What do Roman numerals in a compound mean?

Answer 11

It shows the oxidation number

Question 12

What do ionic half equations show?

Answer 12

They either show reduction or oxidation

Question 13

How do you combine ionic half equations?

Answer 13

You can combine them to make full equations of redox reactions. you do this by balancing out the electrons on each equation.

Question 14

What is reaction rate?

Answer 14

Reaction rate is defined as the change in concentration of a reactant or product over time.

Question 15

How do you calculate the rate of reaction?

Answer 15

amount of reactant used or product formed/time.

Question 16

What is collision theory?

Answer 16

Collision theory is the theory that particles in liquids and gases are always moving and colliding with each other. For a reaction to take place particles must collide with the correct orientation as well as having sufficient activation energy.

Question 17

What is activation energy?

Answer 17

Activation energy is the minimum amount of kinetic energy that particles need to react.

Question 18

Overall what does a Maxwell-Boltzmann distribution curve show?

Answer 18

It shows that molecules in a gas don’t all have the same activation energy. If you plotted a graph of the numbers of molecules in a gas with different kinetic energies you would get the identifiable curve.

Question 19

What does the area under a Maxwell-Boltzmann distribution curve represent?

Answer 19

The area under the curve is equal to the total number of molecules in the system.

Question 20

Why does the Maxwell-Boltzmann distribution curve start at (0,0) ?

Answer 20

No molecules have zero energy

Question 21

What does the peak of the Maxwell-Boltzmann distribution curve represent?

Answer 21

The peak of the curve represents the most likely energy of any single molecule. This tends to be the area where most molecules reside.

Question 22

What do the far right molecules, past the line indicating activation energy represent on a Maxwell-Boltzmann distribution curve?

Answer 22

They represent the number of molecules with enough activation energy that are able to react.

Question 23

What happens to the Maxwell-Boltzmann distribution curve when you increase the temperature?

Answer 23

Increasing temperature means the particles on average will have more kinetic energy. So a greater proportion of molecules will have at least the activation energy and be able to react. This pushes the curve to the right and area under the graph after activation energy increases so more molecules have the correct activation energy.

Question 24

Why do higher temperatures increase the rate of reaction?

Answer 24

• more molecules have the correct activation energy
• molecules are travelling faster so they will collide more often/more frequent collisons

Question 25

Why does increasing concentration also increase the rate of reaction?

Answer 25

If you increase the concentration of reactants in a solution the particles will on average be closer together. If they are closer together they'll collide more often. If collisions occur more frequently, they'll have more chances to react. This is why increasing concentration increases reaction rate.

Question 26

Why does increasing pressure increase the rate of reaction?

Answer 26

If a reaction involves gases, increasing the pressure works in just the same way as increasing concentration. Raising the pressure pushes all the gas particles closer together, making them more likely to collide so collisions take place more frequently, and the reaction rate increases.

Question 27

What is a catalyst?

Answer 27

A catalyst is a substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of a reaction.

Question 28

How do you measure reaction rates by timing how long a precipitate takes to form?

Answer 28

- you can use this method when the product is a precipitate which clouds a solution - you watch a mark through the solution and time how long it takes to be obscured - - if the same observer uses the same mark each time, you can compare the rates of reaction, because the same amount of precipitate will have been formed when the mark becomes obscured

Question 29

How do you measure reaction rates by measuring a decrease in mass?

Answer 29

- when one more of the products is a gas, you can measure the rate of formation using a mass balance - As gas is given off, the mass of the reaction mixture decreases

Question 30

How do you measure reaction rates by measuring the volume of gas given off?

Answer 30

- This involves using a gas syringe to measure the volume of gas being produced - You can only use this method when one or more of the products is a gas.

Question 31

How would you measure the rate of reaction between sodium thiosulfate and hydrochloric acid?

Answer 31

- measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder - use a water bath to gently heat both solutions to the desired temperature before you mix them - mix the solutions in a conical flask. Place the flask over a black cross which can be seen through the solution. Watch the black cross disappear through the cloudy sulfur and time how long it takes - The reaction can be repeated at different temperatures keeping the same depth

Question 32

What is dynamic equilibrium?

Answer 32

When the rate of the forward reaction is equal to the rate of the backward reaction, dynamic equilibrium is when the concentrations of reactants and products stay constant. Dynamic equilibrium can only happen in a closed system.

Question 33

What factors can you change to alter the position of equilibrium?

Answer 33

- concentration - pressure - temperature

Question 34

What is le chatelier's principle?

Answer 34

If a reaction at equilibrium is subjected to a change in concentration, pressure, or temperature, the position of equilibrium will move to counteract the change.

Question 35

What happens in a reversible reaction if you increase the concentration of the products?

Answer 35

If you increase the concentration of the product, the equilibrium tries to remove the extra product. This makes the reverse reaction go faster. So the equilibrium shifts to the left.

Question 36

What happens in a reversible reaction if you increase the concentration of the reactants?

Answer 36

If you increase the concentration of a reactant, the equilibrium tries to get rid of the extra reactants. It does this by making more products so the equilibrium shifts to the right.

Question 37

What happens when you increase pressure in a reversible reaction?

Answer 37

Increasing the pressure shifts the equilibrium to the side with fewer gas molecules. This reduces the pressure.

Question 38

What happens when you decrease pressure in a reversible reaction?

Answer 38

Decreasing the pressure shifts the equilibrium to the side with more gas molecules/ This raises the pressure again.

Question 39

What happens when you increase the temperature in a reversible reaction?

Answer 39

Increasing the temperature means adding heat. The equilibrium shifts in the endothermic direction to absorb this heat.

Question 40

What happens when you decrease the temperature in a reversible reaction?

Answer 40

Decreasing the temperature means removing heat. The equilibrium shifts in the exothermic direction to produce more heat, in order to counteract the drop in temperature.

Question 41

What effects do catalysts have on the position of equilibrium?

Answer 41

Catalysts have no effect on the position of equilibrium. They can't increase yield- but they do mean that equilibrium is reached faster.