Kinetics and Equilibria (CHEM4)

Contains questions of acids, bases and pH, kinetics, equilibria, and tirtrations

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  • Created by: L :)
  • Created on: 07-02-14 09:34
What is a NUCLEOPHILE?
An electron pair donor
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What is an ELECTROPHILE?
An electron pair acceptor
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What is ADDITION?
Adding another group onto a molecule
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What is SUBSTITION?
Swapping one group on a molecule for another
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Why does BENZENE undergo ELECTROPHILIC SUBSTITUTION?
If not the delocalised system would be broken and the molecule would no longer be stable
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What is an ACID?
Proton donor
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What is a BASE?
Proton acceptor
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What is the definition of pH?
-log(H+) - where (H+) is the concentration of H+ ions
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What is the IONIC PRODUCT OF WATER?
Kw=(H+)(OH-) - in water H+ = OH-
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What is a BUFFER SOLUTION?
A solution that resists changes in pH when small amounts of acids or bases are added to it
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How do you make and ACIDIC BUFFER?
Acid + Salt of the acid (Na)
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Give and example of an ACIDIC BUFFER?
Ethanoic Acid (CH3COOH) + Sodium Ethanoate (CH3COONa)
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How do you make a BASIC BUFFER?
Base + Salt of the base (Cl)
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Give an example of a BASIC BUFFER?
Ethly Amide (CH3CH2NH2) + Ethlyammonium chloride (HC3CH2NH3Cl)
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How do you find the pH of a WEAK ACID?
Ka=(H+)(A-)/(HA) - rearrange to get H+ which is equal to A- the -log(H+)
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How do you find the pH of a BUFFER?
H+ = Ka x (ACID)/(SALT)
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Where are BUFFERS USED?
Shampoo's, washing powders, in our bodies
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How do you find the change in pH when adding H+?
H+ = Ka x (ACID+X)/(SALT-X) - this is done using no. of moles so must be changed back into conc.
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How do you find the change in pH when adding OH-?
H+ = Ka x (ACID-X)/(SALT+X) - where X is no. of moles of OH-
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Define a STRONG ACID?
An acid that dissociates fully in solution
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Define a STRONG BASE?
A base that dissociates fully in solution
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What do WEAK ACIDS and BASES do?
Only partially dissociate
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What form does the RATE EQUATION take?
R = K x(A)^m x (B)^n - where A and B are concentrations, and K is the rate constant
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What effect does TEMERATURE have of the RATE CONSTANT?
When temperature increases so does K and when it decreases so does K
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What are 'm' and 'n' in the RATE EQUATION?
The orders of A and B e.g order 2 means 'squared' effect of concentration
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What is the overall ORDER of a reaction?
m + n (the powers of A and B added)
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What effect does something ORDER 0 have on the rate?
Has no effect on the rate (anything to the power of 0 is one)
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What does the RATE EQUATION show us?
The effect that different reactants have on the rate of the reaction
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Define RATE OF REACTION?
The change in concentration of reactants or products per unit of time
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What is the RATE DETERMINING STEP?
The slowest step in a multi-step reaction
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How can you identify the RATE DETERMINING STEP?
It contains everything in the rate equation, or something derived from it
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Define DYNAMIC EQUILIBRIUM?
The rate of the forwards and reverse reactions are equal and the concentrations of reactants and products remains constant
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What type of system must it be for DYNAMIC EQUILIBRIUM to happen?
Closed so that nothing can get in or out
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State LE CHATILER PRINCIPLE?
When a change is applied to a reaction at dynamic equilibrium the position of equilibrium will shift to oppose the change
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What effect does INCREASED TEMPERATURE have of equilibrium?
The position will shift towards the endothermic reaction to oppose the change
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What effect does DECREASED TEMPERATURE have on equilibrium?
The equilibrium will shift towards the exothermic reaction to oppose the change
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What effect does a CATALYST have on equilibirum?
No effect, it just increases the rate at which equlibrium is reached
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What is the EQUILIBIRUM CONSTANT?
Kc = (C)^c X (D)^d / (A)^a X (B)^b - comes from the equation A^a + B^b -> C^c + D^d
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What can cause the value of Kc to change?
Temperature only - it is fixed at a given temperature
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What happens when Kc increases?
More product is formed
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What happens when Kc decreases?
Less product is formed
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How do you work out NUMBER OF MOLES in a titration?
n = C X V
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What is the END POINT in a titration?
Where the acid/base is just neutralised - has a very steep gradient
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How would you identify a SUITABLE INDICATOR?
The indicator must have a colour change across the end point
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How can you find the end point for a WEAK ACID & WEAK BASE titration and why?
Must use a pH meter as there is no sharp pH change
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What is a titration used for?
To work out the concentration of something
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Other cards in this set

Card 2

Front

What is an ELECTROPHILE?

Back

An electron pair acceptor

Card 3

Front

What is ADDITION?

Back

Preview of the front of card 3

Card 4

Front

What is SUBSTITION?

Back

Preview of the front of card 4

Card 5

Front

Why does BENZENE undergo ELECTROPHILIC SUBSTITUTION?

Back

Preview of the front of card 5
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