6.1 Physical and Chemical Changes
1. How are physical and chemical changes identified?
Physical changes do not result in the formation of new chemical substances and are often easily reversible, while chemical changes involve the formation of one or more new substances and are usually more difficult to reverse.
2. What are the primary differences between physical and chemical changes?
A physical change involves a change in state or form without changing the chemical identity of the substance, whereas a chemical change involves a rearrangement of atoms to create new products with different properties.
6.2 Rate of Reaction
3. What is the effect of changing the concentration of solutions on the rate of reaction?
Increasing the concentration increases the rate of reaction.
4. How does changing the pressure of gases affect the rate of reaction?
Increasing the pressure of gaseous reactants increases the rate of reaction.
5. What happens to the rate of reaction when the surface area of solid reactants is changed?
Increasing the surface area of a solid (by breaking it into smaller pieces) increases the rate of reaction.
6. Describe the effect of temperature on the rate of reaction.
Increasing the temperature increases the rate of reaction.
7. What is the effect of adding or removing a catalyst, including enzymes, on the rate of reaction?
Adding a catalyst increases the rate of reaction, while removing it would cause the rate to return to its uncatalyzed speed.
8. Define a catalyst.
A substance that increases the rate of a reaction and remains chemically unchanged at the end of the reaction.
9. List two practical methods for investigating the rate of a reaction.
Measuring the change in mass of a reactant or a product over time, and measuring the volume of a gas formed over time.
10. How is the rate of reaction interpreted from an experimental data graph?
The steepness (or gradient) of the slope represents the rate of reaction; the steeper the line, the faster the reaction is occurring. For curved graphs, the rate at a specific point can be determined by calculating the gradient of a tangent drawn to the curve.
11. Describe collision theory in terms of the number of particles.
Collision theory considers the number of particles per unit volume in a system.
12. How does collision theory define the frequency of collisions?
It refers to how often particles collide with each other per unit of time.
13. What role does kinetic energy play in collision theory?
Particles must have sufficient kinetic energy to overcome the activation energy barrier during a collision for a reaction to occur.
14. Relate activation energy (Ea) to collision theory.
A collision is only "effective" or successful if the colliding particles possess energy equal to or greater than the activation energy.
15. Explain the effect of concentration on reaction rate using collision theory.
Increasing concentration increases the number of particles per unit volume, which increases the frequency of collisions between particles.
16. Explain the effect of gas pressure on reaction rate using collision theory.
Increasing pressure increases the number of gas particles per unit volume, leading to an increased frequency of collisions.
17. Explain the effect of solid surface area on reaction rate using collision theory.
Increasing the surface area exposes more particles to collisions, thereby increasing the frequency of collisions.
18. Explain the effect of temperature on reaction rate using collision theory.
Increasing temperature increases the kinetic energy of particles, making them move faster and collide more frequently; additionally, a higher proportion of particles will have energy greater than the activation energy.
19. Explain the effect of a catalyst on reaction rate using collision theory.
A catalyst increases the rate by providing an alternative reaction pathway with a lower activation energy (Ea), meaning more particles have enough energy to react upon collision.
6.3 Reversible Reactions and Equilibrium
20. What symbol is used to show that a chemical reaction is reversible?
The symbol ⇌.
21. Describe the effect of heat on hydrated copper(II) sulfate.
Heating hydrated copper(II) sulfate drives off the water to form anhydrous copper(II) sulfate; the color changes from blue to white.
22. Describe the effect of adding water to anhydrous copper(II) sulfate.
Adding water to white anhydrous copper(II) sulfate turns it back into blue hydrated copper(II) sulfate.
23. Describe the effect of heat on hydrated cobalt(II) chloride.
Heating hydrated cobalt(II) chloride turns it from pink to blue anhydrous cobalt(II) chloride.
24. Describe the effect of adding water to anhydrous cobalt(II) chloride.
Adding water to blue anhydrous cobalt(II) chloride turns it back into pink hydrated cobalt(II) chloride.
25. When is a reversible reaction in a closed system at equilibrium regarding reaction rates?
When the rate of the forward reaction is equal to the rate of the reverse reaction.
26. When is a reversible reaction in a closed system at equilibrium regarding concentration?
When the concentrations of reactants and products are no longer changing.
27. Predict how increasing temperature affects the position of equilibrium.
Increasing temperature shifts the equilibrium in the direction of the endothermic reaction.
28. Predict how decreasing temperature affects the position of equilibrium.
Decreasing temperature shifts the equilibrium in the direction of the exothermic reaction.
29. Predict how increasing pressure affects the position of equilibrium in a gaseous reaction.
Increasing pressure shifts the equilibrium toward the side with the fewer number of gas molecules.
30. Predict how decreasing pressure affects the position of equilibrium in a gaseous reaction.
Decreasing pressure shifts the equilibrium toward the side with the greater number of gas molecules.
31. Predict how changing concentration affects the position of equilibrium.
Increasing the concentration of a reactant shifts the equilibrium toward the products; increasing product concentration shifts it toward the reactants.
32. What is the effect of using a catalyst on the position of equilibrium?
A catalyst has no effect on the position of equilibrium; it only increases the rate at which equilibrium is reached.
33. State the symbol equation for the Haber process.
N2(g) + 3H2(g) ⇌ 2NH3(g)
34. What are the sources of hydrogen and nitrogen for the Haber process?
Hydrogen is sourced from methane, and nitrogen is sourced from the air.
35. State the typical conditions used in the Haber process.
450 °C, 20,000 kPa (200 atm), and an iron catalyst.
36. State the symbol equation for the conversion of sulfur dioxide to sulfur trioxide in the Contact process.
2SO2(g) + O2(g) ⇌ 2SO3(g)
37. What are the sources of sulfur dioxide and oxygen for the Contact process?
Sulfur dioxide is sourced from burning sulfur or roasting sulfide ores, and oxygen is sourced from the air.
38. State the typical conditions for the sulfur trioxide stage of the Contact process.
450 °C, 200 kPa (2 atm), and a vanadium(V) oxide catalyst.
39. Why are the specific typical conditions chosen for the Haber and Contact processes?
They are chosen to balance the rate of reaction, the yield (position of equilibrium), safety considerations, and economic costs.
6.4 Redox
40. What is used to indicate the oxidation number of an element in a compound?
A Roman numeral.
41. Define a redox reaction.
A reaction that involves simultaneous oxidation and reduction.
42. Define oxidation and reduction in terms of oxygen.
Oxidation is the gain of oxygen, and reduction is the loss of oxygen.
43. How are redox reactions identified in terms of oxygen?
By identifying which substances gain oxygen (oxidized) and which lose oxygen (reduced).
44. Define oxidation and reduction in terms of electrons.
Oxidation is the loss of electrons, and reduction is the gain of electrons.
45. Define oxidation and reduction in terms of oxidation number.
Oxidation is an increase in oxidation number; reduction is a decrease in oxidation number.
46. How are redox reactions identified in terms of electrons?
By identifying reactions where electrons are gained and lost.
47. What is the oxidation number of an element in its uncombined state?
Zero.
48. What is the oxidation number of a monatomic ion?
It is the same as the charge on the ion.
49. What is the sum of the oxidation numbers in a neutral compound?
Zero.
50. What is the sum of the oxidation numbers in a complex ion?
It is equal to the charge on the ion.
51. How can redox reactions be identified using acidified aqueous potassium manganate(VII)?
By a color change from purple to colorless, indicating that the manganate(VII) ion has been reduced (it is an oxidising agent).
52. How can redox reactions be identified using aqueous potassium iodide?
By a color change from colorless to brown, indicating that the iodide ion has been oxidized to iodine (it is a reducing agent).
53. Define an oxidising agent.
A substance that oxidises another substance and is itself reduced.
54. Define a reducing agent.
A substance that reduces another substance and is itself oxidised.
55. How are oxidising and reducing agents identified in a reaction?
By determining which substance loses electrons/increases in oxidation number (reducing agent) and which gains electrons/decreases in oxidation number (oxidising agent).