Rate Of Reactions

Question 1

What is the ‘rate’ of a chemical reaction?

Answer 1

-A measure of how quickly the reactants are converted into products

Question 2

What are the formulas for rate of reaction

Answer 2

-rate of reaction= amount of reactant used/time
-rate of reaction=amount of product formed/time

Question 3

what can the quantity of reactant be measured in?

Answer 3

mass in grams

Question 4

What can quantity of product be measured in?

Answer 4

volume in cm^3

Question 5

What are the units of rate of reaction?

Answer 5

g/s or cm^3/s

Question 6

How do scientists determine the exact rate of reaction?

Answer 6

-using tangents

Question 7

What is the collision theory?

Answer 7

-chemical reactions can only take place when reacting particles collide with each other. The collisions must have sufficient energy

Question 8

What is the rate of a chemical reaction determined by?

Answer 8

-the frequency of successful collisions

Question 9

What does frequency mean

Answer 9

-the number of successful collisions per second

Question 10

Describe the relationship between rate and concentration

Answer 10

-if the concentration increases so does the rate
-the rate is proportional to the concentration

Question 11

What are the five factors which affect the rate of chemical reactions?

Answer 11

-concentration
-pressure
-surface area
-temperature
-catalysts

Question 12

What is the activation energy?

Question 13

What happens if we increase the concentration of reactants in solutions?

Answer 13

-increases the frequency of collisions and so increases the rate of reaction

Question 14

What happens if we increase the pressure of reacting gases

Answer 14

-increases the frequency of collisions and so increases the rate of reaction

Question 15

What happens if we increase the surface area of solid reactants?

Answer 15

-increases the frequency of collisions and so increases the rate of reaction

Question 16

What happens if we increase the temperature?

Answer 16

-increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.

Question 17

What is a catalyst?

Answer 17

-substances that speed up chemical reactions without being changed or used up during the reaction

Question 18

What do enzymes act as?

Answer 18

-enzymes act as catalysts in biological systems

Question 19

How does sulfur affect the solution?

Answer 19

-sulfur makes the solution go cloudy.
-scientists call this cloudiness turbidity
-we can use this to see how long the reaction takes to finish

Question 20

What is the method for the disappearing cross experiment practical

Answer 20

-use a measuring cylinder to put 10cm^3 of sodium thiosulfate solution into a conical flask
-place the conical flask onto a printed black cross
-add 10cm^3 of hydrochloric acid into the conical flask
-swirl the solution and start a stopwatch
-solution will turn cloudy and we stop clock when we can no longer see cross
-carry out experiment again using lower concentrations of sodium thiosulfate solution
-repeat the whole experiment and calculate mean values for each concentration of sodium thiosulfate solution.

Question 21

When is a measurement reproducible?

Answer 21

-if it can be repeated by another person
-or using a different technique or equipment and still getting the same result.

Question 22

what is the problem with the disappearing cross experiment?

Answer 22

-different people have different eyesights.

Question 23

What is the method to measure the volume of the gas produced by a reaction?

Answer 23

-use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flask
-attach the conical flask to a bung and delivery tube
-now place the delivery tube into a container filled with water
-place upturned measuring cylinder also filled with water over the delivery tube.
-add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch.
-the reaction produces hydrogen gas which trapped in measuring cylinder
-every ten seconds, measure the volume of hydrogen gas in measuring cylinder
-continue until no more hydrogen is given off.
-repeat experiment using different concentrations of hydrochloric acid

Question 24

How do catalysts affect the activation energy?

Answer 24

-catalysts decrease the activation energy: this increases the proportion of particles with energy to react
-catalysts provide a different pathway for a chemical reaction that has a lower activation energy.

Question 25

Describe and explain the effect of increasing temperature on the rate of reaction

Answer 25

-as temperature increases, kinetic energy of particles increase leading to more energetic collisions -also, they move faster, so they collide more frequently -rate and temperature are not directly proportional to each other.

Question 26

Describe and explain the effect of increasing concentration on the rate of reaction

Answer 26

-concentration increase leads to faster reaction -more reactants lead to more frequent collisions

Question 27

Describe and explain the effect of increasing pressure of a gas on the rate of reaction

Answer 27

-it increases the number of gas molecules in the same volume and so increases frequency of collisions and therefore increases the rate of reaction -volume and pressure are inversely proportional to each other

Question 28

Describe and explain the effect of increasing surface area

Answer 28

-if solid reactants are in smaller pieces, they have a greater surface area. -increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction -block of magnesium reacts slower with acid then magnesium powder

Question 29

What is a reversible reaction?

Answer 29

-when the products of a reactant can react backwards to produce the original reactants

Question 30

When is dynamic equilibrium reached?

Answer 30

-in a closed system, when the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant

Question 31

Describe Le Chatelier’s principle

Answer 31

-if a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium

Question 32

Describe the effect of changing temperature on the position of the equilibrium

Answer 32

-if the temperature of a system at equilibrium is increased : •the relative amount of products at equilibrium increases for an endothermic reaction -the relative amount of products at equilibrium decreases for an exothermic reaction

Question 33

Describe the effect of changing the concentration of reactant and product on the position of the equilibrium

Answer 33

-if the concentration of one of the reactants or products are changed , the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again. -if the concentration of a reactant is increased, more products will be formed until equilibrium is reached again. -if the concentration of a product is decreased,more reactants will react until equilibrium is reached again

Question 34

Describe the effect of changing pressure on the position of equilibrium

Answer 34

-an increase in pressure causes the equilibrium position to shift toward the side with the smaller number of molecules as shown by the symbol equation for that reaction. -A decrease in pressure causes the equilibrium position to shift toward the side with the larger number of molecules as shown by the symbol equation for that reaction -pressure has no effect on the reactions where the numbers of gas molecules are equal on both sides of the equation

Question 36

Describe the effect of a catalyst on the position of the equilibrium

Answer 36

-no effect -it just speeds up both forward and backward reactions equally