topic 7: rates of reaction and energy changes

Question 1

activation energy

Answer 1

the minimum amount of energy that particles must collide with to react

Question 2

catalyst

Answer 2

something that increases the rate of reaction by providing a pathway for the reaction that has a lower activation energy. they are not used up during the reaction.

Question 3

collision theory

Answer 3

chemical reactions only occur when colliding particles collide with the correct orientation and with sufficient energy

Question 4

displacement

Answer 4

a chemical reaction in which a more reactive element displaces a less reactive element from its compound

Question 5

effect of concentration on reaction rate

Answer 5

increasing the concentration of reactants in solution means the reacting particles will be closer together. this means they will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction

Question 6

effect of pressure on reaction rate

Answer 6

increasing the pressure of gaseous reactants means the reacting particles will be closer together. this means they will collide more often so there will be a higher rate of successful collisions and a faster rate of reaction.

Question 7

effect of surface area of reaction rate

Answer 7

increasing the surface area of the reactants means there are more exposed reacting particles. this means there are more frequent successful collisions so the rate of reaction increases

Question 8

effect of temperature on reaction rate

Answer 8

increasing the temperature means the particles will have more kinetic energy and so will move faster. if the molecules are moving faster they will collide more often, and since they’ve gained kinetic energy, a larger proportion of the particles will have at least the activation energy. for both these reasons the rate of reaction increases.

Question 9

endothermic reaction

Answer 9

a reaction that takes in energy from the surroundings so the temperature of the surroundings decreases. in an endothermic reaction the energy needed to break existing bonds is greater than the energy released from forming new bonds

Question 10

enzymes

Answer 10

biological catalysts which speed up biochemical reactions so that organisms can survive. they are used in the production of alcoholic drinks

Question 11

exothermic reaction

Answer 11

a reaction that transfers energy to the surroundings so the temperature of the surroundings increases in an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds

Question 12

neutralisation

Answer 12

the reaction in which an acid and a base react to form a salt and water

Question 13

overall energy change of the reaction

Answer 13

the difference between the sum of energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed

Question 14

precipitation reactions

Answer 14

a reaction in which solutions react to form an insoluble product

Question 15

rate of reaction

Answer 15

the measure of the amount of product formed or reactant used over time. the units of rate of reaction may be given as g/s, cm³/s or mol/s

Question 16

reaction profile

Answer 16

graphs used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction