Rates, equilibrium and pH

sophie.holland96
Flashcards by sophie.holland96, updated more than 1 year ago
sophie.holland96
Created by sophie.holland96 over 7 years ago
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OCR Chemistry A spec

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Question Answer
Rate of Reaction The change in concentration of a reactant or product per unit time
How do you write a rate equation? rate = k[A][B] (the order in respect to the reactant is shown as the power)
Half-life The time taken for the concentration of the reactant to reduce by half (first order = constant half-life)
What does the rate-concentration graph look like for a zero order reactant?
What does the rate-concentration graph look like for a first order reactant?
What does the rate-concentration graph look like for a second order reactant?
Rate-determining step The slowest step in the reaction mechanism of a multi-step reaction
What is the general expression for Kc
Dynamic equilibrium When the rate of the forward reaction is equal to the rate of the backward reaction, in a closed system.
Standard conditions 298K 100kPa (1atm) 1moldm^-3
Homogenous equilibrium An equilibrium in which all the species making up the reactants and products are in the SAME state
Kc only changes with Temperature
If Kc is more than one the equilibrium shifts to the ... Right and favours the products
If Kc is less than 1 the equilibrium shifts to the... Left and favours the reactants
How is Kc value affected by temperature? Increase in Kc - rise in temp if the forward reaction is endothermic (equilibrium shift to the right) Decrease in Kc - rise in temp if the forward reaction if exothermic (equilibrium shift to the left)
An acid A proton donor
A base A proton acceptor
Alkali A base that dissolved in water to form OH- ions
Neutralisation A chemical reaction in which an acid and a base react together to produce a salt and water
Acid + Carbonate = salt + carbon dioxide + water ( remember - the ionic equation varies with states of the carbonate)
Acid-base pair A pair of two species that transform into each other by gain or loss of a proton
What is the general expression for the acid dissociation constant (Ka)?
How do you work out the pH of a STRONG acid? [H+] = [HA] (due to complete dissociation) pH = -log [H+]
How do you calculate the pH of a WEAK acid?
What is the expression for the ionic product of water, Kw?
What are the two methods for calculating the pH of a strong base? pOH and Kw (remember [OH-] = base concentration due to complete dissociation)
What is a buffer solution? A mixture of a weak acid (HA) and its conjugate base (A-) that minimises pH changes on addition of small amounts of acid or base.
General buffer equation.
How do you work out the [H+] of a buffer solution? (which can then be used to calculate the pH)
Define equivalence point The point in a titration at which the volume of one solution has reacted exactly with the volume of a second solution (there are no reactants in excess)
The end point is... The point in a titration is the point at which the indicator changes colour. (the point at which there are equal concentrations of the weak acid and conjugate base forms of the indicator)
What indicator would be used for a strong acid - weak base titration? And state the colour change Methyl orange Red (acid) --> Orange --> Yellow (base)
What indicator would be used for a weak acid - strong base titration? And state the colour change. Phenolphthalein pink (base) --> colourless (acid) Very sudden change
Titration curve: Where is the equivalence point?
Define enthalpy change of neutralisation The energy change that accompanies the neutralisation of an aqueous acid by an aqueous base/alkali to form one mole of water under standard conditions.
Determining enthalpy change of neutralisation. How do you work out the energy change? (m = mass of solutions)
Calculate enthalpy change of neutralisation. Remember: n = moles of limiting reactant
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