Chemical Equilibrum 1-3 Flashcards
What is Equilibrum?
A chemical reaction is in equilibrum when the rate of the forward and backward reactions are the same. At equilibrum the concentrations of the reactants and products are constant but not equal.
What can affect the position of equilibrum?
1) Concentration of reactants or products.
2) Changing the pressure if there are moles of gas on both sides of the equation.
3) Changing the temperature.
What happens when a catalyst is added?
The rate at which equilibrum is established speeds up but there is no effect on the position of equilibrum.
For the general equation aA + bB —> cC + dD what is the expression for K?
K = (C)c(D)d/(A)a(B)b
What units does K have?
None.
What is a homogenous and heterogenous equilibrum?
Homogenous - All species are in the same state at equilibrum.
Heterogenous - All species are in different states at equilibrum.
What value are pure solids and liquids given in the expression for K?
1
Does changing the concentration or pressure effect K?
No, because the posiiton of equilbrum is quickly re-established until the ratio of reactants to products returns to its original value (K is quickly re-established).
Does adding a catalyst effect K?
No. Because the presence of a catalyst has no effect on the position of equilibrum, it doesn’t have an effect on K either.
What is the effect of temperature on K?
- For an endothermic reaction, an increase in temperature favours the products, meaning K wil increase.
- For an exothermic reaction, an increase in temperature favours the reactants, meaning K will decrease.
What is a hydrogen atom after it loses its electron?
A proton, but in water they are hydrated protons with the formula H3O+. Another word for hydrated protons is hydronium ions.
What is Kw?
The equilibrum/dissociation constant for the ionisation of water which is also called the ionic product of water. It has the expression Kw=(H+)(OH-). As it is a constant, its value is dependent on temperature and at 24 degrees celsius its value is 1 x 10^-14.
What does amphoteric mean?
An amphoteric substance is something that can act as an acid and a base such as water.
What is the relationship between pH/pOH and hydrogen/hydroxide ion concentration?
pH= -log10(H+) or pOH= -log10(OH-).
What happens to the hydrogen ion concentration when pH increases by a factor of one and two units?
When pH increases by a factor of one, the H+ concentration increases by a factor of ten and when the pH increases by a factor of two the H+ concentration increases by a factor of 100.
What is a strong acid?
A strong acid is an acid that is completely dissociated in aqueous solution. The solution will consist of ions only with none of the reactants left.
What are some examples of strong acids?
Hydrochloric acid, nitric acid, sulfuric acid.
What is a weak acid?
A weak acid is an acid that is only partially dissociated in aqueous solution. Usually the equilibrum lies to the reactant side, meaning the value of K is less than one, so there are mostly reactants in the solution and not many ions.
What are some examples of weak acids?
All carboxylic acids, carbonic acid, sulfurous acid.
What are monoprotic and diprotic acids?
Monoprotic acids contain only one hydrogen per molecule which can become a hydrogen ion e.g. hydrochloric acid. Diprotic acids contain two hydrogens per molecule which can become hydrogen ions. e.g. sulfurous acid.
What is a strong base?
A strong base is completely ionised in aqueous solution. There are no reactant molecules in the solution, only the products.
What are some examples of strong bases?
Oxides and hydroxides of the alkali metals, and soluble oxides and hydroxides of the group 2 metals.
What is a weak base?
A weak base is only partially ionised in aquous solution. The equilibrum usually lies to the left meaning K will be less than one and the solution won’t contain many ions.
What are some examples of weak bases?
Ammonia and ammines.
