Unit 5 Chem Mini-Quiz Study Guide

5.1: Reaction Rates

• The rate of a reaction is equal to the rate of a reactant divided by its coefficient.

• The rate of a reactant is change concentration/change time

• Higher molarity, higher temp (higher energy vs. activation energy), higher SA, homogenous catalysts (alt. pathway less energy) or heterogenous (lower E_A by orientation)

• Convert from one rate of reaction to another with mole ratios (may be negative if needed) and can use 6% as molarity (0.06)

5.2: Introduction to Rate Law

• When table, no coefficient! Order = sum degrees

• Based on factor of multiplication, figure out degree by power

• If, based on the table, can’t find experiment where one constant, one not:

  • Ratio of everything with superscripts; eventually evaluate to get unknown

• To find k, plug in experiment

• k unit is 0th: m/time, then 1/M^(n-1)time

5.3: Concentration Changes Over Time

• Zeroth Order: linear

  • Rate= -ΔA/Δt = k

  • Integrated Rate Law: [A]= [A₀ ]- kt

  • Straight line plot is just -k

  • Half/life is A₀/2k

• First Order: exponential; Look for constant ½ lives!

  • Rate= -ΔA/Δt=k[A]

  • Smooth curve exponential graph

  • Integrated Rate Law: ln [A ]= ln [A₀] - kt

  • Straight line plot: ln [A]; slope -k

  • Half/life is 0.693/k

• Second Order: Sharp exp; Half-lives decrease.

  • Rate= -ΔA/Δt = k [A]²

  • Integrated Rate Law: 1/[A] = 1/[A₀] + kt

  • Straight line plot 1/A, just k

  • Half/life is 1/k[A₀]

5.4: Elementary Reactions

• Reactions multi steps (uni vs. bi vs. termolecular = number particles involved)

• Rate dependent slow step

5.5: Collision Model

• Collision Theory: for a reaction

  • Particles must collide (high M = high collisions)

  • Must have sufficient energy (over E_a); heat = more

  • Particles must be in the correct orientation, but if not over E_a, but still no react

• Increasing temp. by 10^oC usually doubles reaction rate

• M-B graph flattens as temp up

5.6: Reaction Energy Profile

• The peak length from reactants to products is E_^a

• Exothermic = negative deltaH, products lower

• Endothermic = positive deltaH, products higher

• Catalysts lower E_a

5.7-5.9: Introduction to Reaction Mechanisms

• Combine to get overall; cancel catalysts (prod) and intermediates (used)

• Rate law on slow step; if slow step contains intermediate, use another step (assume fast, equilibruim) to replace with other terms

5.10 and 5.11: Multistep Reaction Energy Profile

• Make sure represents overall reaction; E_a subsequent between low point and high point; highest E_a is rate determining

• Peaks = number steps

• Catalysts: may increase collisions/lower E_A (enzymes)

  • Shifts E_a left; more particles can be over

  • May produce new intermediates can new elementary steps that need less energy