Chemistry A2 Level

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Author:
koolcookie11
ID:
119051
Filename:
Chemistry A2 Level
Updated:
2011-12-26 11:06:53
Tags:
Rates equilibria pH
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Description:
Rates, Equilibrium and pH Unit 2
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  1. Rate of Reaction
    • the change in concentration of a reactant or product per unit time
    • measures: how fast reactants are being used up and how fast products are being made
    • Units: mol dm-3 s-1
    • Concentration-time graphs:
    • gradient of tangent shows rate of reaction
    • when t=0 gradient is the initial rate
  2. Orders
    • the power to which the concentration of the reactant is raised in the rate equations
    • Zero order: rate is unaffected by changing the concentration
    • First order: rate is proportional to concentration
    • Second order: if concentration increases by 2 then the rate increases by 22=4
  3. Rate constant, k
    • the constant that links the rate of reaction with the concentrations of the reactants raised to the power of their orders in the rate equation
    • effect of temperature: increasing temperature, speeds up the rate of reaction, increasing the rate constant, k
  4. Rate equation
    • rate=k[A]0[B]1[C]2...
    • is also equal to rate=k[B][C]2
    • overall order is the sum of the individual orders
    • Units: k=rate/[A]: s-1
    • k=rate/[A]2: dm3 mol-1 s-1
    • k=rate/[A]2[B]: dm6 mol-2 s-1
  5. Half-life
    • the time taken for the concentration of a reactant to reduce by half
    • a first order reaction has a constant half life
    • the half life of a first order reaction is independent of the concentration (half life is the same no matter what the concentration is)
    • Zero order: half life decreases with time
    • Second order: half lif increases with time
  6. Rate-determining step
    • the slowest step in a multi-step reaction
    • the order with respect to the reactant tells you how many particles of the reactant are involved in the rate-determining step
  7. Equiibrium
    • Equilibrium constant, Kc=products/reactants
    • Units: mol dm-3
    • Temperature change: increase temperature equilibrium shifts in the endothermic direction (+ve), decrease exothermic direction
    • if more product is formed Kc will increase
    • Kc is unaffected by concentration or pressure change, or by a catalyst
  8. Bronsted-Lowry
    • Acid: proton donor
    • Base: proton acceptor
    • Reactions:
    • Conjugate acid-base pairs: a pair of two species that transform into each other by gain or loss of a proton
  9. Strong and weak acids
    • Strong acid: an acid that completely dissociates in solution
    • Weak acid: an acid that partially dissociates in solution
    • Acid dissociation constant, Ka shows the extent of acid dissociation a large Ka means the acid is strong
    • pKa=-log10Ka
    • Ka=10-pKa
  10. pH and [H+(aq)]
    • pH=-log[H+]; [H+]=10-pH
    • Kw=[H+][OH-]
  11. Buffers
    • Buffer solution: a system that minimises pH changes on addition of small amounts of an acid or base, can be made up from a weak acid and a salt of the weak acid
    • Example: CH3COOH/CH3COONa

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