Chapter 10 Equilibrium & Reaction Rates Flashcards
What is ‘rate of reaction’?
Measures how fast a reactant is being used up or how fast a product is being formed.
Can be defined as the change in concentration of a reactant or product in a given time.
- fastest at start (each reactant is at highest concentration)
- slows down (reactants are being used up)
- = 0 (once one of the reactants has been completely used up)
What factors can affect the reaction rate?
(1) concentration (or pressure for gases)
(2) temperature
(3) use of catalyst
(4) surface area (for solid reactants)
What does collision theory state?
That 2 reacting particles must collide for a reaction to occur.
- usually only a small proportion of collisions result in a chemical reaction
- most collisions = molecules collide, bounce off, and remain chemically unchanged
What 2 conditions need to be met for an EFFECTIVE collision?
- particles collide with correct ORIENTATION
- particles have sufficient energy to overcome the activation energy BARRIER of the reaction
Effect of concentration on reaction rate??
An increase in concentration increases the number of reacting particles in the same volume. The particles are pushed closer together and collide more frequently. Therefore, in a given period of time there will be a higher proportion of effective collisions (w/ correct orientation and sufficient energy).
= INCREASED reaction rate
Effect of pressure (of gas) on reaction rate??
When a gas is compressed into a smaller volume, the pressure increases. The concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume. … more collision = higher proportion are effective …
How can you follow the progress of a reaction?
(1) monitoring the removal of a reactant
(2) following the formation of a product
- method chosen depends on the properties and physical states of reactants and products
What is a catalyst and what does it do?
A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.
- NOT USED UP
- may form an INTERMEDIATE product or provide a surface in which the reaction can take place
- end of reaction, catalyst is REGENERATED
= it increases the rate of a chemical reaction by providing an alternative reaction pathway with LOWER activation energy
What is a HOMOGENEOUS catalyst?
Has the SAME physical state as the reactants.
1) The catalyst reacts with the reactants to form an intermediate.
2) The intermediate then breaks down to give the product and regenerates the catalyst
What is a HETEROGENEOUS catalyst?
Has a DIFFERENT physical state from the reactants.
1) reactant molecules are ADSORBED (weakly bonded) onto the surface of the catalyst, where the reaction takes place.
2) after reaction… the product molecules leave the surface of the catalyst via DESORPTION
Define the Boltzmann distribution?
The spread of molecular energies in gases.
NO molecules have zero energy - the curve starts at the origin.
AREA under curve = TOTAL number of molecules
NO MAX energy for a molecule - the curve does NOT meet the x0axis at high energy
- would need to reach infinite energy for curve to meet x-axis
What is the effect of temperature on the Boltzmann distribution curve?
As temperature increases, the average energy of molecules increases. A small proportion of molecules will still have a low energy, but more molecules have a higher energy.
- the graph is stretched over a greater range of values
- peak of the graph is lower on the y-axis
- peak of the graph is further along the x-axis (at a higher energy)
- number of molecules stays the same - area under the graph is the same
What is the effect of catalysts on the Boltzmann distribution curve?
A catalyst provides an alternative reaction route with a lower activation energy.
Dotted line for activation energy = lower down on x-axis
- more molecules have sufficient energy now
What are reversible reactions?
Reactions that take pace in BOTH forwards and reverse directions.
Describe dynamic equilibrium?
Rate of forward = Rate of reverse
Concentration of reactants and products remain the same DO NOT CHANGE
DYNAMIC = at equilibrium both reactions are taking place
MUST be in a CLOSED SYSTEM (no outside influences)
