topic 6 - the rate and extent of chemical change

Question 1

What are reversible reactions?

Answer 1

Reversible reactions are chemical reactions where the products can react to reproduce the original reactants.

Question 2

How can the direction of a reversible reaction be changed?

Answer 2

The direction of a reversible reaction can be changed by altering the conditions such as temperature or pressure.

Question 3

What symbol is used to represent a reversible reaction?

Answer 3

The symbol used to represent a reversible reaction is ‘⇌’ instead of ‘→’.

Question 4

Give an example of a reversible reaction.

Answer 4

An example of a reversible reaction is the Haber Process which converts hydrogen and nitrogen into ammonia: N₂ + 3H₂ ⇌ 2NH₃.

Question 5

What happens to energy in reversible reactions during an endothermic process?

Answer 5

If a reversible reaction is endothermic in one direction it is exothermic in the opposite direction meaning energy is absorbed in one case and released in the other.

Question 6

Is the amount of energy transferred the same in both directions of a reversible reaction?

Answer 6

Yes the same amount of energy is transferred in both directions; however one direction will absorb energy while the other will release it.

Question 7

What is meant by equilibrium in the context of reversible reactions?

Answer 7

Equilibrium is reached when the rates of the forward and reverse reactions are equal in a closed system resulting in a stable concentration of reactants and products.

Question 8

What is the significance of a closed system in reversible reactions?

Answer 8

A closed system is significant because it allows the equilibrium to be established without the interference of outside factors ensuring accurate rates of reaction can be measured.

Question 9

How does temperature affect the direction of a reversible reaction?

Answer 9

Increasing temperature typically favors the endothermic reaction (forward direction) while decreasing temperature favors the exothermic reaction (reverse direction).

Question 10

What is Le Chatelier’s principle?

Answer 10

Le Chatelier’s principle states that if a system at equilibrium experiences a change in concentration temperature or pressure the system will shift in a direction that counteracts the change in order to restore equilibrium.

Question 11

How does changing the concentration of reactants affect a chemical equilibrium?

Answer 11

If the concentration of reactants is increased the position of the equilibrium shifts towards the products. This means that more product will be produced until a new equilibrium is reached. Conversely if the concentration of reactants is decreased the position will shift towards the reactants.

Question 12

What happens to equilibrium when the concentration of products is increased?

Answer 12

If the concentration of products is increased the position of equilibrium shifts towards the reactants resulting in the production of more reactants until a new equilibrium is established.

Question 13

How does temperature affect chemical equilibrium?

Answer 13

Increasing the temperature of an exothermic reaction shifts the position of equilibrium to favor the reactants. For an endothermic reaction increasing temperature shifts the equilibrium to favor the products.

Question 14

What is the impact of increasing temperature on an exothermic reaction at equilibrium?

Answer 14

In an exothermic reaction if the temperature is increased the position of equilibrium shifts to the left towards the reactants and the production of products decreases.

Question 15

In an endothermic reaction what happens when temperature is decreased?

Answer 15

In an endothermic reaction decreasing the temperature shifts the position of equilibrium to the left towards the reactants resulting in the production of fewer products.

Question 16

What is the reaction quotient (Q) and how is it related to equilibrium?

Answer 16

The reaction quotient (Q) is a measure of the relative concentrations of products to reactants at a specific point in time. If Q is different from the equilibrium constant (K) the system is not at equilibrium and will shift in the direction that alters Q towards K.

Question 17

What does it mean for a system to be at equilibrium?

Answer 17

A system is at equilibrium when the rates of the forward and reverse reactions are equal resulting in constant concentrations of reactants and products over time.

Question 18

How does pressure change affect equilibrium in gaseous reactions?

Answer 18

Increasing the pressure will shift the equilibrium position towards the side of the reaction with fewer moles of gas while decreasing pressure favors the side with more moles of gas.

Question 19

What factors can affect the position of equilibrium in a chemical reaction?

Answer 19

The position of equilibrium can be affected by changes in concentration temperature and pressure.

Question 20

Explain how dilution of a solution affects equilibrium. What happens to the concentration of reactants and products?

Answer 20

Dilution decreases the concentration of all species in the solution. The system will shift towards the side that has more moles of solute in order to counteract the decrease in concentration.

Question 21

What is the significance of the equilibrium constant (K)?

Answer 21

The equilibrium constant (K) is a numerical value that describes the ratio of the concentrations of products to reactants at equilibrium at a specific temperature. It provides insight into the extent of the reaction and whether reactants or products are favored at equilibrium.

Question 22

What happens to the equilibrium position of an endothermic reaction when the temperature is increased?

Answer 22

For an endothermic reaction increasing the temperature shifts the equilibrium to the right favoring the formation of more products.

Question 23

What occurs to the equilibrium position of an endothermic reaction when the temperature is decreased?

Answer 23

When the temperature is decreased the equilibrium shifts in the direction of the exothermic reaction favoring the formation of reactants.

Question 24

Define ‘yield’ in the context of a chemical reaction.

Answer 24

Yield refers to the amount of product produced from a chemical reaction indicating the efficiency of the reaction.

Question 25

What effect does an increase in temperature have on the yield of an endothermic reaction?

Answer 25

An increase in temperature increases the yield of an endothermic reaction.

Question 26

What effect does a decrease in temperature have on the yield of an endothermic reaction?

Answer 26

A decrease in temperature decreases the yield of an endothermic reaction.

Question 27

How does pressure influence the equilibrium position of gaseous reactions?

Answer 27

In gaseous reactions an increase in pressure favors the reaction that produces the least number of molecules.

Question 28

In the reaction N2 + 3H2 ⇌ 2NH3 what happens to equilibrium when the pressure is increased?

Answer 28

When the pressure is increased in this reaction the equilibrium shifts to the right side (towards the products) as there are fewer moles of gas on the right (2 moles of NH3) compared to the left (4 moles: 1 N2 + 3 H2).

Question 29

What does it mean if a reaction is classified as exothermic?

Answer 29

An exothermic reaction releases energy in the form of heat to the surroundings during the reaction.

Question 30

What happens to the equilibrium position of an exothermic reaction when the temperature is increased?

Answer 30

Increasing the temperature of an exothermic reaction causes the equilibrium to shift to the left favoring the formation of reactants.

Question 31

What happens to the equilibrium position of an exothermic reaction when the temperature is decreased?

Answer 31

Decreasing the temperature of an exothermic reaction shifts the equilibrium to the right favoring the formation of more products.

Question 32

What are the implications of Le Chatelier's principle in terms of changes to a chemical system?

Answer 32

Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions the position of equilibrium shifts to counteract the change.

Question 33

How does a decrease in pressure affect equilibrium in a reaction with more moles of gas on the left-hand side?

Answer 33

A decrease in pressure will shift the equilibrium to the side of the equation with more moles of gas. In this case it would shift left producing more reactant.

Question 34

What is the effect of increasing pressure on the yield of a reaction that produces a larger volume of gas?

Answer 34

An increase in pressure decreases the yield of the reaction if it produces a larger volume of gas as the equilibrium would shift toward the side with fewer moles of gas.

Question 35

How does a decrease in pressure affect the yield of a reaction that produces fewer moles of gas on the right-hand side?

Answer 35

A decrease in pressure increases the yield of the reaction if it produces fewer moles of gas as the equilibrium shifts toward the side with more gas moles.

Question 36

Define the rate of reaction in terms of reactants and products.

Answer 36

The rate of reaction can be defined as the change in concentration mass or volume of reactants or products per unit time. It is measured by the amount of reactant used or product formed over time.

Question 37

What are the two methods to measure the rate of reaction?

Answer 37

The rate of reaction can be measured in two ways: by the amount of reactant used over time or by the amount of product formed over time.

Question 38

How can the quantity of reactants or products be measured in a chemical reaction?

Answer 38

The quantity of reactants or products can be measured by the mass in grams or by the volume in cm³.

Question 39

What are the possible units for the rate of reaction?

Answer 39

Units of the rate of reaction may include grams per liter per second (g/L/s) moles per liter per second (mol/L/s) or any appropriate unit that reflects the change over time.

Question 40

What does an equilibrium shift to the right entail in terms of reactants and products?

Answer 40

An equilibrium shift to the right entails the formation of more products from the reactants resulting in the increased concentration of the products.

Question 41

Why do changes in pressure affect the equilibrium position in a reaction involving gaseous reactants and products?

Answer 41

Changes in pressure affect the equilibrium position because gases occupy space and changes in pressure favor the side of the reaction that minimizes the number of moles of gas present.

Question 42

What is the relationship between the number of gas moles and the effect of pressure on chemical equilibrium according to Le Chatelier's Principle?

Answer 42

According to Le Chatelier's Principle if the pressure changes the equilibrium will shift toward the side that has fewer moles of gas to counteract the change thus minimizing the effect of increased pressure.

Question 43

What is the definition of the rate of reaction in terms of reactants?

Answer 43

The rate of reaction can be expressed in terms of the quantity of reactants consumed or products formed per unit time commonly measured in mol/s.

Question 44

What are the possible units for the rate of reaction?

Answer 44

The rate of reaction can be expressed in various units such as grams per second (g/s) centimeters cubed per second (cm³/s) or moles per second (mol/s).

Question 45

How can the rate of reaction be measured graphically?

Answer 45

The rate of reaction can be measured graphically by drawing tangents to curves on reaction graphs and calculating the slope of the tangent.

Question 46

What does the gradient of a tangent represent on a reaction graph?

Answer 46

The gradient of a tangent to the curve on a reaction graph represents the rate of reaction at a specific time.

Question 47

List the main factors that affect the rates of chemical reactions.

Answer 47

The main factors that affect the rates of chemical reactions are: concentration pressure surface area temperature and the presence of catalysts.

Question 48

Explain collision theory in relation to chemical reactions.

Answer 48

Collision theory states that chemical reactions can only take place when reacting particles collide with one another and these collisions must occur with sufficient energy to overcome the activation energy barrier.

Question 49

What is activation energy?

Answer 49

Activation energy is the minimum amount of energy that reacting particles must possess in order to successfully collide and react.

Question 50

How does increasing the concentration of reactants affect the rate of reaction?

Answer 50

Increasing the concentration of reactants in solution increases the frequency of collisions among particles which accelerates the rate of the reaction.

Question 51

What effect does increasing the pressure of reacting gases have on the rate of reaction?

Answer 51

Increasing the pressure of reacting gases compresses the gas particles leading to more frequent collisions and increasing the rate of reaction.

Question 52

How does surface area impact the rate of reaction in solid reactants?

Answer 52

Increasing the surface area of solid reactants allows for more particle collisions to occur which increases the rate of reaction.

Question 53

What role do catalysts play in chemical reactions?

Answer 53

Catalysts increase the rate of chemical reactions by providing an alternative pathway with a lower activation energy thus allowing more collisions to result in reactions.

Question 54

What effect does increasing temperature have on the rate of a chemical reaction?

Answer 54

Increasing the temperature increases the frequency of collisions between reactant molecules and makes the collisions more energetic which leads to an increased rate of reaction.

Question 55

What are catalysts?

Answer 55

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

Question 56

How do enzymes function as catalysts in biological systems?

Answer 56

Enzymes act as catalysts in biological systems by facilitating reactions and lowering the activation energy required for the reaction to occur.

Question 57

Are catalysts included in the chemical equation for a reaction?

Answer 57

No catalysts are not included in the equation for a reaction since they are not consumed or changed by the reaction.

Question 58

How do catalysts affect activation energy?

Answer 58

Catalysts decrease the activation energy required for a reaction which increases the proportion of reactant particles that have enough energy to react.

Question 59

What is one key benefit of using a catalyst in a chemical reaction?

Answer 59

One key benefit of using a catalyst is that it provides a different pathway for a chemical reaction that has a lower activation energy allowing the reaction to occur more easily.

Question 60

What role do catalysts play in reaction kinetics?

Answer 60

Catalysts play a crucial role in reaction kinetics by increasing the reaction rate without altering the overall equilibrium of the reaction.

Question 61

Can catalysts change the position of equilibrium in a chemical reaction?

Answer 61

No catalysts do not change the position of equilibrium; they only help the system reach equilibrium faster.

Question 62

What is activation energy in the context of chemical reactions?

Answer 62

Activation energy is the minimum energy required for reactant molecules to collide and undergo a reaction.

Question 63

Explain the term 'reaction rate'.

Answer 63

'Reaction rate' refers to the speed at which reactants are converted into products in a chemical reaction.