24012018

Question 1

Heat of solution

Answer 1

• When some compounds (e.g. NaOH) dissolve in water, a lot of heat is released
  > The container gets hot > dissolving process = exothermic
• When other compounds (e.g. NH4NO3) dissolve in water, heat is absorbed frm the surroundings
  > The container gets cold > dissolving process = endothermic

Question 2

Energetics of solution formation: the enthalpy of solution

Answer 2

• To make a solution, steps:
  1) Overcome all attractions btw solute particles
  > Change in H_solute = endothermic
  2) Overcome some attractions btw solvent molecules
  > Change in H_solvent = endothermic
  3) Form new attractions btw solute particles + solvent molecules
  > Change in H_mix = exothermic
  »> The overall Change in H for making a solution depends on relative sizes on the Change in H for these 3 processes
  Change in H_solution
  = Change in H_solute + Change in H_solvent + Change in H_mix

Question 3

Energetics of solution formation: exothermic

Answer 3

-If the total energy cost for breaking attractions btw particles in the pure solute and pure solvent is
LESS THAN the energy released in making the new attractions btw the solute and solvent
> Overall process = exothermic

Question 4

Energetics of solution formation: endothermic

Answer 4

-If the total energy cost for breaking attractions btw particles in the pure solute and pure solvent is
GREATER THAN the energy released in making the new attractions btw the solute and solvent
> Overall process = endothermic

Question 5

Heats of hydration

Answer 5

• For aq solution of ionic compounds.
  Energy added to overcome attractions btw water molecules
  And energy released in forming attraction btw water molecules and ions
  Are combined to a term
  > Heat of hydration
• Attractive forces btw ions = lattice energy
  Change in H_solute = - Change in H_lattice energy
• Attractive forces in water = H bonds
• Attractive forces btw ion and water = ion-dipole
• Change in H_hydration = heat released when 1 mol of gaseous ions dissolve in water = Change in H_solvent + Change in H_mix

Question 6

*Heat of solution VS Heat of hydration

Answer 6

• Becoz lattice energy is ALWAYS exothermic
  > size and sign on the change in H_soln tells us something abt Change in H_hydration
• If heat of solution is large + endothermic
  > Then amount of energy it costs to separate ions is more than energy released from hydrating ions
  Change in H_hydration < Change in H_lattice when Change in H_soln is (+)
• If heat of solution is large + exothermic
  > Then amount of energy it costs to separate ions is less than energy released from hydrating ions
  Change in H_hydration > Change in H_lattice when Change in H_soln is (-)

Question 7

Heats of solution for ionic compounds

Answer 7

• Change in H_solution = Change in H_solute + Change in H_solvent + Change in H_mix
• Change in H_solution = - Change in H_lattice + Change in H_solvent + Change in H_mix
• Change in H_solution = Change in H_hydration - Change in H_lattice
• Change in H_solution = -Change in H_lattice + Change in H_hydration

Question 8

Chp 14 Chemical Kinetics

Answer 8

-

Question 9

Reaction rates

Answer 9

• Chem kinetics = study of how fast reactions to place
• Some happen almost instantaneously, while others can tk millions of yrs
• Increasing rate of a reaction is important to many industrial processes

Question 10

Collision theory of chem reactions

Answer 10

• Most reactions happen faster at higher temp
• Chem reactions generally occur as a result of collisions btw reacting molecules
• Collision theory of chem kinematics:
  > Reaction rate is directly proportional to no. of molecular collisions per second
• Molecules must also be oriented in a way that favors reaction
• e.g. CL + NOCL > Cl2 + NO
  Before collision
  > Collision (Incorrect orientation does not favor reaction)
  > After collision (An ineffective collision results in no reaction)

Question 11

Effective collision

Answer 11

• Collisions that result in a chemical reaction

Question 12

Activation energy (E_a)

Answer 12

• The minimum amount of energy required to initiate a chemical reaction

Question 13

Activated complex (transition state)

Answer 13

• Formed when molecules collide in an effective collision

Question 14

Measuring reaction progress and expressing reaction rate:

Average reaction rate

Answer 14

• A -> B

- rate = - Change in A / Change in t; rate = Change in B / Change in t

Question 15

Average reaction rate

Answer 15

• e.g. Br2 (aq) + HCOOH (aq) > 2Br^- (aq) + 2H^+ (aq) + CO2 (g)
  > Average rate = - Change in Br2 / Change in t
  = - (Br2_final - Br2_initial) / (t_final - t_initial)

Question 16

Instantaneous rate

Answer 16

• The rate for a specific instant in time