# Chemistry A2 Level

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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
 Author: koolcookie11 ID: 119051 Card Set: Chemistry A2 Level Updated: 2011-12-26 16:06:53 Tags: Rates equilibria pH Folders: Description: Rates, Equilibrium and pH Unit 2 Show Answers: