Rate and equilibria Flashcards
What do we look at to measure the rate of a chemical reaction?
How quickly the reactants are used up or how quickly the products of the reaction are made
What are the three ways to take the measurements of the rate of a chemical reaction?
Measuring the mass of a reaction mixture
Measuring the volume of gas given off
Measuring the time for a visual change like precipitation
How do we calculate the mean rate of a reaction?
Mean rate of reaction = amount of reactant used or amount of product formed / time
What are the four factors that affect the rate of a chemical reaction?
Temperature
Surface area
Concentration of solutions / pressure of gases
A catalyst
Why do more collisions of particles result in a faster reaction?
Because a higher proportion of particles have energy greater than the activation energy
What is the affect of surface area on the rate of a reaction?
If the surface area of any solid reactant is increased (e.g. crushed up / cut into smaller pieces) then the rate of reaction will increase as this increases the frequency of collisions
What is the affect of temperature on the rate of a reaction?
When we increase the temperature of a reaction it always increases the rate of the reaction because the particles gain more energy, causing more frequent collisions
What are the affects of concentration and pressure on the rate of a reaction?
Increasing the concentration or pressure of reactants increases the number of particles per cm³ which causes the frequency of collisions to increase (increasing the pressure meaning reducing the size of the container of gas)
How does a catalyst work?
It works by providing an alternative route with a lower activation energy, causing more particles to have energy greater than the activation energy and increasing the number of collisions
What are two examples of catalysts?
Iron in the Haber process to make ammonia
Platinum used in the production of nitric acid
Do catalysts have an affect on the position of equilibrium?
They have no effect on the position of equilibrium so they do not alter the composition of the equilibrium mixture
What happens to a reversible reaction in a closed system?
No reactants, products or energy can get in or out
and equilibrium is reached when the rates of both the forwards and backwards reactions become equal
What happens to the position of equilibrium if temperature is raised?
The position of equilibrium moves in the endothermic direction to cool down the system
What happens to the position of equilibrium if temperature is lowered?
The position of equilibrium moves in the exothermic direction to heat up the system
What happens if the concentration of a reactant is increased?
More products will be formed to decrease the concentration of the reactants
What happens if the product concentration is decreased?
More reactants will react to increase the concentration of the products
What happens to the position of equilibrium if pressure is raised?
The position of equilibrium moves to the side with the fewest gas molecules to reduce the pressure
What happens to the position of equilibrium if pressure is lowered?
The position of equilibrium moves to the side with most gas particles to increase the pressure
What is the process of
manufacturing ammonia?
1) Nitrogen from the air and hydrogen from methane are used
2) The purified gases are compressed (at 200 atmospheres) and heated (at 450 degrees celsius)
3) The mixture is passed over a hot catalyst of iron and some of the nitrogen and hydrogen combine to give ammonia
4)The unreacted nitrogen and hydrogen continue to be passed over the catalyst
5) The mixture is cooled and has now formed liquid ammonia
Why can’t we use a higher pressure to form even more ammonia?
Because it would require lots of energy and be expensive
Why can’t we use a lower temperature to form even more ammonia?
Although lower temperatures would increase the amount of ammonia produced, it would be produced too slowly
What affect does a catalyst have on the production of ammonia?
A catalyst does not affect the actual yield of ammonia but we do get it formed quicker
