the rate and extent of chemical change

Question 1

Define rate of reaction

Answer 1

• How fast the reactants are changed into products

Question 2

Name the equation used to calculate/measure the rate of reaction

Answer 2

• Rate of reaction = amount of reactant used / Time
• Rate of reaction = amount of product formed / Time

Question 3

What can the quantity of reactant or product be measured by?

Answer 3

• Mass in grams or volume in cm3

Question 4

What are the units of rate of reaction?

Answer 4

• g/s or cm3/s

Question 5

What are the units for rate of reaction in terms of moles?

Answer 5

• You can also use quantity of reactants in terms of moles (instead of mass or volume) and therefore, units for rate of reaction in mol/s

Question 6

How do you find the rate of reaction graphically?

Answer 6

• To measure the rate of reaction: draw tangents to curves and use the slope of the tangent
• Calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time

Question 7

Describe the relationship between the gradient of the line and the rate of reaction

Answer 7

• The steeper the line on the graph, the faster the rate of reaction
• Over time the line becomes less steep as the reactants are used up

Question 8

Name the factors which affect the rates of chemical reactions

Answer 8

• Concentration
• Pressure
• Surface area
• Temperature
• Catalysts

Question 9

What does the rate of a chemical reaction depend on?

Answer 9

• Collision frequency of reacting particles
• Energy transferred during a collision

Question 10

Define collision theory

Answer 10

• Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy

Question 11

Define activation energy

Answer 11

• The minimum amount of energy that particles must have to react

Question 12

What happens when you increase the concentration of reactants in solution?

Answer 12

• If a solution is more concentrated, it means there are more particles in the same volume of water
• This means that the same number of particles occupy a smaller space
• Increases the frequency of collisions and so increases the rate of reaction.

Question 13

What happens when you increase the pressure of reacting gases?

Answer 13

• If pressure increases, it means there are more particles in the same volume of gas
• This means that the same number of particles occupy a smaller space
• Increases the frequency of collisions and so increases the rate of reaction

Question 14

What happens when you increase the surface area of solid reactants?

Answer 14

• When you break up a solid into smaller pieces it will increase its SA:V ratio
• This means for the same volume of solid, the particles have more area to work on
• Increases the frequency of collisions and so increases the rate of reaction.

Question 15

What happens when you increase the temperature of the reactants?

Answer 15

• When the temp increases, the particles move faster (gain kinetic energy)
• Increases the frequency of collisions and makes the
  collisions more energetic, and so increases the rate of reaction.

Question 16

Define a catalyst

Answer 16

• Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction

Question 17

Define an enzyme

Answer 17

• Enzymes act as catalysts in biological systems

Question 18

Are catalysts included in the equation for a reaction?

Answer 18

• No, catalysts are not included in the equation for a reaction

Question 19

What is the purpose of a catalyst?

Answer 19

• Decrease the activation energy; this increases the proportion of particles with energy to react
• Provide a different pathway for a chemical reaction that has a lower activation energy.

Question 20

What is a reversible reaction?

Answer 20

• Where in​ ​some​ ​chemical​ ​reactions,​ ​the​ ​products​ ​of​ ​the​ ​reaction​ ​can​ ​react​ ​to​ ​produce the​ ​original​ ​reactants
• The​ ​direction​ ​of​ ​the​ ​reaction​ ​can​ ​be​ ​changed​ ​by​ ​changing​ ​the​ ​conditions
  (e.g.​ ​for​ ​forwards​ ​reaction​ ​use​ ​hot​ ​conditions​ ​and​ ​for​ ​reverse​ ​use​ ​cool)

Question 21

Describe what happens in a reversible reaction

Answer 21

• As the reactants react, their concentrations fall, so the forward reaction will slow down
• But as more products are made, and their concentrations rise. the backwards reaction will speed up
• After a while, the forward reaction will be at the same rate as the backwards causing equilibrium

Question 22

What happens if a reversible reaction is at equilibirum?

Answer 22

• There is no overall effect
• The concentrations of reactants and products have reached a balance and won’t change

Question 23

What symbol is used in a reversible reaction?

Answer 23

• Use​ ​the​ ​symbol​ ​⇌​ ​instead​ ​of​ ​→​ ​to​ ​represent​ ​a​ ​reversible​ ​reaction

Question 24

Give an example of a reversible reaction

Answer 24

• ​The​ ​Haber​ ​Process:​ ​hydrogen​ ​+​ ​nitrogen​ ​⇌​ ​ammonia

Question 25

What happens if the equilibrium of a reversible reaction lies to the right?

Answer 25

* The conc of products is greater than reactants

Question 26

What happens if the equilibrium of a reversible reaction lies to the left?

Answer 26

* The conc of the reactants is greater

Question 27

Describe the energy changes in a reversible reaction

Answer 27

* If​ ​a​ ​reversible​ ​reaction​ ​is​ ​endothermic​ ​one​ ​way,​ ​it​ ​is​ ​exothermic​ ​in​ ​the​ ​opposite direction. * The​ ​same​ ​amount​ ​of​ ​energy​ ​is​ ​transferred​ ​each​ ​way​ ​(just​ ​for​ ​one​ ​the​ ​energy​ ​will be​ ​lost​ ​and​ ​for​ ​the​ ​other​ ​the​ ​same​ ​amount​ ​will​ ​be​ ​gained) * The energy transferred from the surrounding by the endothermic reaction is equal to the energy transferred to the surroundings during the exothermic reaction

Question 28

Give an example of endothermic and exothermic in reversible reactions

Answer 28

* Thermal decomposition of hydrated copper sulfate * hydrated copper sulfate <> anhydrous copper sulfate + water * If you heated blue hydrated copper sulfate crystals, it drives the water off and leaves WHITE anhydrous copper sulfate powder (endothermic) * If you add water to the white powder, you get blue crystals (exothermic)

Question 29

When is equilibrium reached in a reaction?

Answer 29

* When​ ​a​ ​reversible​ ​reaction​ ​occurs​ ​in​ ​a​ ​closed​ ​system,​ ​equilibrium​ ​is​ ​reached when​ ​the​ ​reactions​ ​occur​ ​at​ ​exactly​ ​the​ ​same​ ​rate​ ​in​ ​each​ ​direction.

Question 30

Explain Le Chatelier's principle

Answer 30

* The​ ​relative​ ​amounts​ ​of​ ​all​ ​the​ ​reacting​ ​substances​ ​at​ ​equilibrium​ ​depend​ ​on the​ ​conditions​ ​of​ ​the​ ​reaction. * If​ ​a​ ​system​ ​is​ ​at​ ​equilibrium​ ​and​ ​a​ ​change​ ​is​ ​made​ ​to​ ​any​ ​of​ ​the​ ​conditions, then​ ​the​ ​system​ ​responds​ ​to​ ​counteract​ ​the​ ​change​

Question 31

What does the position of equilibrium depend on?

Answer 31

* Pressure * Temp * Concentration

Question 32

What is the effect of changing concentration on equilibrium in a reversible reaction?

Answer 32

* I​f ​the​ ​concentration​ ​of​ ​one​ ​of​ ​the​ ​reactants​ ​or​ ​products​ ​is​ ​changed,​ ​the​ ​system is​ ​no​ ​longer​ ​at​ ​equilibrium​ ​and​ ​the​ ​concentrations​ ​of​ ​all​ ​the​ ​substances​ ​will change​ ​until​ ​equilibrium​ ​is​ ​reached​ ​again.

Question 33

What happens if the concentration of reactants is increased in a reversible reaction?

Answer 33

* If​ ​​concentration​ ​of​ ​reactants​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts towards​ ​products​ ​so​​ ​more​ ​product​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is​ ​reached again * (decrease reactants by making more product)

Question 34

What happens if the concretion of products is increased in a reversible reaction?

Answer 34

* If​ ​​concentration​ ​of​ ​products​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts​ ​towards reactants​ ​so​ ​​more​ ​reactant​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is​ ​reached​ ​again

Question 35

What happens if the concentration of products is decreased in a reversible reaction?

Answer 35

* System tries to increase it again by reducing the amount of reactants

Question 36

What happens if the temperature is increased equilibrium in a reversible reaction?

Answer 36

* If​ ​​temperature​ ​is​ ​increased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​​direction​ ​of​ ​the endothermic​ ​reaction​​ ​(e.g.​ ​if​ ​forwards​ ​reaction​ ​is​ ​endothermic​ ​and temperature​ ​is​ ​increased,​ ​equilibrium​ ​shifts​ ​right​ ​to​ ​produce​ ​more​ ​product) * To decrease the heat, meaning more products for endothermic and fewer for exothermic

Question 37

What happens if the temperature is decreased in a reversible reaction?

Answer 37

* If​ ​​temperature​ ​is​ ​decreased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​​direction​ ​of​ ​the exothermic​ ​reaction to produce more heat * You will get more products for exothermic and fewer for endothermic

Question 38

For an exothermic reaction, what happens when you increase/decrease the temperature?

Answer 38

* An​ ​increase​ ​in​ ​temperature - decreases​ ​yield​ ​of​ ​reaction * A​ ​decrease​ ​in​ ​temperature - increases​ ​yield​ ​of​ ​reaction

Question 39

For an endothermic reaction, what happens when you increase/decrease the temperature?

Answer 39

* An increase in temperature - increases​ ​yield​ ​of​ ​reaction * A decrease in temperature - decreases​ ​yield​ ​of​ ​reaction

Question 40

What is the effect of pressure changes on equilibrium in a reversible reaction?

Answer 40

* In​ ​gaseous​ ​reactions,​ ​an​ ​increase​ ​in​ ​pressure​ ​will​ ​favour​ ​the​ ​reaction​ ​that produces​ ​the​ ​least​ ​number​ ​of​ ​molecules​ ​as​ ​shown​ ​by​ ​the​ ​symbol​ ​equation​ ​for that​ ​reaction.

Question 41

What happens if pressure is increased in a reversible reaction?

Answer 41

* If​ ​​pressure​ ​is​ ​increased​:​ ​equilibrium​ ​shifts​ ​to​ ​​side​ ​of​ ​equation​ ​with​ ​fewer​ ​moles of​ ​gas​ ​(e.g.​ ​N​2​​ ​+​ ​3H2​ ​​ ​​⇌​ ​​2NH​3,​ ​ ​left​ ​side​ ​has​ ​4​ ​moles​ ​of​ ​gas​ ​(1+3)​ ​and​ ​right​ ​has​ ​2 moles​ ​of​ ​gas.​ ​If​ ​you​ ​increase​ ​the​ ​pressure​ ​equilibrium​ ​moves​ ​right​ ​as​ ​there​ ​are fewer​ ​moles​ ​of​ ​gas​ ​on​ ​the​ ​right​ ​hand​ ​side,​ ​making​ ​more​ ​product)

Question 42

What happens if pressure is decreased in a reversible reaction?

Answer 42

* If​ ​​pressure​ ​is​ ​decreased​:​ ​equilibrium​ ​will​ ​shift​ ​to​ ​​side​ ​of​ ​equation​ ​with​ ​more moles​ ​of​ ​gas​​ ​(e.g.​ ​for​ ​previous​ ​example​ ​equilibrium​ ​would​ ​move​ ​left

Answer 43

If​ ​a​ ​reaction​ ​produces​ ​a... An​ ​increase​ ​in​ ​pressure... A​ ​decrease​ ​in​ ​pressure... ...larger​ ​volume​ ​of​ ​gas​ ​(more​ ​moles) Decreases​ ​yield​ ​of​ ​reaction Increases​ ​yield​ ​of​ ​reaction ...smaller volume of gas (fewer moles) Increases​ ​yield​ ​of​ ​reaction Decreases​ ​yield​ ​of​ ​reaction