CHEMISTRY C6: RATES OF REACTION

Question 1

what are the main factors that affect the rate of chemical reactions?

Answer 1

-increasing the concentrations of dissolved reactants increases collisions and the RoR
-increasing pressure is the same as increasing concentration
-increasing temperature raises the frequency of collisions, therefore the RoR increases
-increasing the surface area increases collisions and RoT
-catalysts are used up substances the increase RoR without being used up in the process

Question 2

catalysts aren’t used up in chemical reactions. what does this mean?

Answer 2

-they can be used indefinitely
-they are not found in chemical equations
(they need to be cleaned often - having knock-on environmental impacts

Question 3

different reactions need different catalysts. Here are some examples:

Answer 3

-iron is used in the process to make ammonia
-platinum and palladium are used as catalytic converters in cars
-enzymes catalyse reactions in biological systems

Question 4

why do catalysts often come as powders, pellets or fine gauzes?

Answer 4

these types of substances all have particularly high surface areas

Question 5

what do catalysts lower in reactions?

Answer 5

all catalysts lower the activation energy needs in a reaction

Question 6

catalysts advantages - cost effective

Answer 6

-only a small amount of the catalyst is needs to speed up the reaction a lot
-paying for the catalyst may be cheaper than paying for the energy needed to increase temperature or pressure

Question 7

catalysts advantages - reduced burning of fossil fuels

Answer 7

-by reducing the necessary temperature or pressure, fewer fossil fuels need to be burnt

Question 8

catalysts disadvantage- toxicity

Answer 8

-many are toxic and can escape into the environment and contaminate ecosystems

Question 9

what are the factors that affect rates of reaction?

Answer 9

-temperature
-concentration
-particle size
-use of a catalyst

Question 10

what happens when temperature is increased?

Answer 10

if the temperature is increased, the particles have more energy meaning they will move much quicker. RoR increases as the collide more often

Question 11

what happen when concentration is increased?

Answer 11

when the concentration of reactants are increased there will be more particles; and collisions will occur more often, increasing RoR

Question 12

what happens when the particle size is increased?

Answer 12

when a particle’s size is decreased, it increases it’s surface area; causing more collisions and then the RoR will be increasd

Question 13

what happens when a catalyst is used?

Answer 13

a catalyst increases the rate of reaction but isn’t used up. when a catalyst is present, the reacting particles collide more successfully

Question 14

how do you calculate the rate of reaction?

Answer 14

to measure the average rate:

                      change in quantity average rate = —————————
                         change in time