Unit 2- Physical chemistry Flashcards
When is a chemical reaction in equilibrium?
When the composition of the reactants and products remains constant indefinitely
What value is given to the concentrations of pure solids and pure liquids at equilibrium?
They are taken as constant and given a value of 1
What does the numerical value of the equilibrium constant depend on, and what is it not affected by?
Depends on temperature
Not affected by concentration and/or pressure
What is a endothermic reaction?
Reactions that take in energy from their surroundings, the enthalpy change is positive
What is a exothermic reaction?
Reactions that transfer energy to their surroundings, the enthalpy change is negative
For an endothermic reaction what affect does an increase in temperature have an the K value and the yield of product?
The K value increases and the product yield increases
For an exothermic reaction what affect does an increase in temperature have an the K value and the yield of product?
The K value decreases and the product yield decreases
Does the presence of a catalyst affect the value of the equilibrium constant?
No
Water is said to be amphoteric, what is meant by this term?
It can react as an acid and a base
What is the dissociation constant for the ionisation of water known as?
The ionic product
What are the Bronsted-Lowry definitions of acids and bases?
An acid in a proton donor and a base is a proton acceptor
What can be said about acids and bases in a reaction?
For every acid there is a conjugate base, formed by the loss of a proton and for every base there is a conjugate base formed by the gain of a proton
What happens to strong acids and strong bases in aqueous solution?
They dissociate completely into ions
What happens to weak acids and weak bases in aqueous solution?
They only partially dissociate into ions
What are 3 examples of strong acids?
- hydrochloric acid (HCl)
- sulfuric acid (H2SO4)
- nitric acid (HNO3)
What are 3 examples of weak acids?
- ethanoic acid
- carbonic acid
- sulfurous acid
What are an example of a strong base?
Solutions of metal hydroxides e.g. aluminium hydroxide
What are 2 examples of weak bases?
- ammonia
- amines
What do a soluble salt of a strong acid and a strong base produce when dissolved in water?
A neutral solution
What do a soluble salt of a weak acid and a strong base produce when dissolved in water?
An alkaline solution
What do a soluble salt of a strong acid and a weak base produce when dissolved in water?
An acidic solution
What is a buffer solution?
One in which the pH remains approximately constant when small amounts of acid, base or water are added
What does an acid buffer consist of?
A solution of a weak acid and one of its salts made from a strong base
What does a basic buffer consist of?
A solution of a weak base and one of its salts
What are indicators?
Weak acids
In aqueous solution what should the colour of an acid indicator be distinctly different from?
The colour of its conjugate base
How can suitable indicators be selected?
From pH data, including titration curves
What is the standard enthalpy of formation?
The enthalpy change when one mole of a substance is formed from its elements in their standard states
What is the standard state of a substance?
Its most stable state at a pressure of 1 atmosphere and at a specified temperature, usually taken as 298 K
What is the entropy of a system a measure of?
The degree of disorder of the system
What is the relationship between the degree of disorder and entropy?
The greater the degree of disorder, the greater the entropy
What can be said about the disorder of solids and gases?
Solids have low disorder and gasses have high disorder
What happens to entropy when temperature increases?
Entropy increases
At what points is their a rapid increase in the entropy of a substance?
There is a rapid increase in entropy at a the melting point of a substance and then an even more rapid and larger change in entropy at the boiling point
What does the second law of thermodynamics state?
The total entropy of a reaction system and its surroundings always increases for a spontaneous process
What does heat energy released by the reaction system lead to?
An increase in the entropy of the surroundings
What does heat energy absorbed by the reaction system lead to?
A decrease in the entropy of the surroundings
What does the third law of thermodynamics state?
The entropy of a perfect crystal at 0 K is zero
What is the standard entropy of a substance?
The entropy value for the substance in its standard state
If the change in free energy between reactants and products is negative what can be said?
A reaction may occur and the reaction is said to be feasible
What is a feasible reaction?
One which tends towards the products rather than the reactants
At equilibrium what is the value of free energy?
zero
What does the rate of a chemical reaction depend on?
The concentrations of the reactants
What is the overall order of a reaction?
The sum of the powers to which the concentrations of the reactants are raised in the rate equation
What is the rate of reaction dependent on?
The slowest step, which is called the “rate determining step”
What does the equilibrium constant (K) characterise?
The equilibrium composition of the reaction mixture
What does the value of the equilibrium constant (K) indicate?
The position of equilibrium
What units do equilibrium constants have?
None, they don’t have units
What value are the concentrations of pure liquids and pure solids at equilibrium given in the equilibrium equation?
They are taken as a constant and given a value of 1
What does the ionic product vary with?
Temperature
What is H3O+ ?
A hydronium ion (a hydrated proton). A shorthand representation is H+
What is the ionic product of water (approximately) at 25*c?
1 x 10 ^-14 (in databook)
What is enthalpy?
The energy stored in chemical bonds
How can the order of reaction be determined?
Only from experimental data
