Kinetics

Question 1

define rate of reaction

Answer 1

• how quickly a reaction happens
• the rate of change in concentration
• depends on how quickly the concentration of reactant or product changes with time

Question 2

Rate of reaction equation

Answer 2

increase in product conc/ time taken
OR
decrease in reactant con/time taken

Question 3

What unit is rate expressed in?

Answer 3

moldm-3s-1

Question 4

What does a curved graph instead of a straight line tell us?

Answer 4

the gradient is not constant

Question 5

How can you measure the rate of reaction on a graph?

Answer 5

draw a tangent to the curve at the time asked for

Question 6

Why is the rate of reaction greater at the start of the reaction?

Answer 6

There is a greater reactant concentration

Question 7

How would you measure rate of reaction if:

a. reaction produces colored precipitate
b. reaction produces gas

Answer 7

a. measure change in color

b. measure change in volume or mass of gas

Question 8

Explain how to set up 2 experiments to measure the volume of gas produced.

Answer 8

• gas syringe moves outwards as gas collects

- gas collected by displacement of water from inverted burette. Gas has to have low solubility in water

Question 9

Explain how to set up experiment measuring the change in mass.

Answer 9

• on digital balance, set beaker with cotton wool to prevent escape of liquid and solid
• but some gases are too light to show changes in mass
• needs continuous readings

Question 10

kinetic molecular theory

Answer 10

particles in a substance move randomly because of the kinetic energy they possess

Question 11

Do all particles in a substance have the same energy?

Answer 11

No. The random nature of movement and collisions means particles will have a range of energy values

Question 12

What is the best way to measure the kinetic energy of a substance?

Answer 12

Take the average of the energy values of each molecule, and relate it to absolute temperature (temp measured in kelvin)

Question 13

What does the Maxwell- Boltzmann distribution curve show?

Answer 13

Particles in a gas at a particular temperature show a range in their kinetic energy values

Question 14

What is plotted on x and y axis in Maxwell-Boltzmann distribution curve?

Answer 14

x- kinetic energy

y- number of particles with kinetic energy

Question 15

How do reactions occur?

Answer 15

• reactants placed together
• kinetic energy that particles possess cause them to collide with each other
• result: bonds between reactants broken, bonds form. Thus, products form

Question 16

What is the collision theory?

Answer 16

• particles must collide
• particles must have sufficient energy
• particles must collide with correct orientation

Question 17

What do many collisions lack?

Answer 17

Sufficient energy and correct orientation to break bonds of reactant

Question 18

Activation Energy

Answer 18

energy required for reaction to take place

Question 19

What are the factors affecting the rate of reaction?

Answer 19

• temperature
• concentration
• particle size
• pressure
• catalyst

Question 20

Why is activation energy necessary?

Answer 20

• to overcome repulsion between molecules

- to break some bonds in reactants before they can react

Question 21

Draw and label an endothermic graph

Answer 21

(look in book)

Question 22

Draw and label an exothermic graph

Answer 22

(look in book)

Question 23

Which particles can have successful collisions?

Answer 23

Particles that have a kinetic energy value greater than the activation energy will have successful collisions.

Question 24

Do reactions with high or low activation energy proceed faster?

Answer 24

• high Ea reactions are slow

- low Ea reactions are faster

Question 25

Explain the affect of temperature on the rate of reaction

Answer 25

increase in temp - increase in average kinetic energy - increase in collisions, moving faster - higher proportion of molecules have activation energy, more successful collisions +affects sufficient energy and collision frequency

Question 26

Explain the affect of particle size on the rate of reaction

Answer 26

- decreasing particle size (increasing surface area) increases rate of reaction, i.e. powder +affects collision frequency

Question 27

Explain the affect of pressure on the rate of reaction

Answer 27

- increases number of collisions +affects frequency of collisions

Question 28

Explain the affect of a catalyst on the rate of reaction

Answer 28

- increase rate of reaction by lowering Ea, by providing an alternate pathway - lower reaction energy by providing surface for reaction and weakening bonds +affects collisions

Question 29

Explain the affect of concentration on the rate of reaction

Answer 29

-increase concentration: increases rate of reaction +affects collision frequency and successful collisions

Question 30

How do catalysts lower reactivation energy?

Answer 30

- Providing surface for reaction | - Weakening bonds of reactants

Question 31

What is the effect of temperature on a Maxwell- Boltzman distribution graph?

Answer 31

- at higher temperature- more particles have kinetic energy value greater than Ea - at low temperature- less particles have kinetic energy value greater than Ea

Question 32

Define and state the advantage and disadvantage to heterogenous catalysts.

Answer 32

- catalysts in different state than reactant - easy to remove - doesn't spread easily

Question 33

Define and state the advantage and disadvantage to homogenous catalysts.

Answer 33

- same state as reactant - mixes easily - difficult to remove`

Question 34

State the techniques for measuring the rates of reaction. (6 ways)

Answer 34

Measuring - change in volume of gas - change in mass - change in transmission of light: colorimetry/ spectrophometry - change in concentration measured by titration - change in concentration measured using conductivity - non-continuous methods of detecting change during a reaction - clock reactions

Question 35

Describe how to measure the rates of reaction through the change in transmission of light.

Answer 35

- indicator added sometimes to generate color - colorimeter or spectrometer passes light of specific wavelength through solution - measures intensity of light transmitted by reaction components - substances with higher concentration absorb more light, therefore transmitting less - photocell generates electric current according to light transmitted - continuous readings - determine rate of reaction by measuring decrease in absorbance

Question 36

Describe how to measure the rate of reaction through the change in concentration measured using titration.

Answer 36

- measure concentration of one of reactants or products by titrating it against known standard - no continous readings - identify: reactant and product includes water

Question 37

Describe how to measure the rate of reaction through the change in concentration measured using electricity

Answer 37

- electrical conductivity or a solution depends on total concentration of its ions and charges - measured using conductivity meter - measure difference in concentration of ions between reactants and products - decrease in concentration of ions- decrease in electrical conductivity - identify: metals, Br, Al

Question 38

Describe how to measure the rate of reaction through the non-continuous methods of detecting change during a reaction: clock reactions

Answer 38

- measure time it takes for reaction to reach observable fixed point - enact same reaction under different conditions, find different timings, and judge different rates of reaction

Question 39

True or false: are rate and time indirectly proportional?

Answer 39

True- rate= 1/time