Unit 3

Question 1

What is the collision theory?

Answer 1

for a chemical reaction to take place the reactant particles must collide

Question 2

What things is needed for collisions to be successful?

Answer 2

Correct geometry, enough energy to overcome the activation energy

Question 3

What is activation energy?

Answer 3

the energy required for a reaction to take place

Question 4

what is the definition of the activated complex?

Answer 4

an unstable arrangement of atoms

Question 5

Where is the activated complex on an energy diagram?

Answer 5

very top of the curve

Question 6

How can we increase the speed of reactions, what happens to the particles?

Answer 6

increase temp- gives particles energy, more successful collisions.
increase concentration- more particles, more successful collisions

Question 7

What does a catalyst do in a reaction?

Answer 7

• speeds up reaction by providing alternative route and lowering activation energy
  =>if less energy is required for successful collisions then more collisions are likely to happen

Question 8

What happens to the activation energy if we increase the temperature?

Answer 8

nothing

Question 9

What is a homogeneous catalyst?

Answer 9

a catalyst that’s in the same physical state as the reactants

Question 10

What is a heterogeneous catalyst?

Answer 10

a catalyst that’s in a different physical state from the reactants

Question 11

What are the names of the three stages of how heterogeneous catalyst’s work?

Answer 11

1. Adsorption
2. reaction
3. desorption

Question 12

Give a summary of each stage of how heterogeneous catalysts work?

Answer 12

1. Adsorption- absorbing reacting molecules on active site & holds with weak bonds. causes bonds within molecule to weaken.
2. reaction- reaction occurs with less activation energy to form activated complex
3. desorption- product molecules are formed and leaves catalyst’s surface

Question 13

What is catalyst poisoning?

Answer 13

when another substance attaches to active site. irreversible

Question 14

What is an exothermic reaction?

Answer 14

a reaction that releases heat (-ve)

Question 15

What is an endothermic reaction?

Answer 15

a reaction that takes in heat (+ve)

Question 16

What is enthalpy change?

Answer 16

energy difference between products and reactants

Question 17

How can we tell on an energy diagram if the reaction is exothermic or endothermic?

Answer 17

EXOTHERMIC- products lower than reactants
ENDOTHERMIC- products higher than reactants

Question 18

Definition of enthalpy of combustion

Answer 18

energy released when 1 mole of a substance is completely burned in oxygen

Question 19

What are the products of complete combustion?

Answer 19

water and carbon dioxide

Question 20

What are the sources of error for experimental vs theoretical values?

Answer 20

• not enough oxygen for complete combustion
• some fuel evaporates
• no lid on container
• if water has not been stirred
• some heat energy absorbed by beaker

Question 21

How can a bomb calorimeter be used to improve the experiment?

Answer 21

• heat no longer lost to surroundings
• complete combustion occurs

Question 22

What is molar bond enthalpy?

Answer 22

energy required to break one mole of chemical bonds in the gaseous state and form two moles of gaseous atoms

Question 23

What id mean bond enthalpies?

Answer 23

bonds that are found in more than one substance

Question 24

What are the steps of finding enthalpy change

Answer 24

1. draw full structural formula to show all bonds
2. write a list of all bonds broken (+) in reactants
3. write a list of bonds made (-) in products
4. write in bond enthalpy values for each
5. calculate total energies
6. calculate enthalpy change using equation

Question 25

What is Hess's law?

Answer 25

Hess's ;aw states that the enthalpy change for a chemical reaction is independent of the route taken

Question 26

What is a closed system?

Answer 26

where reactants and products are not aloud to escape

Question 27

What happens in a reaction when it reaches equilibrium?

Answer 27

at equilibrium the reactants change into products at exactly the same rate at which the products change into reactants. this only occurs in a closed system. The reaction has NOT stopped

Question 28

what is dynamic equilibrium?

Answer 28

in a closed system, when the rate of the foward and reverse reactions are equal, and the concentrations of products and reactants are constant

Question 29

How do chemists maxamise product?

Answer 29

chemists employ strategies to change the position of the equilibrium in favor of the products

Question 30

What is le chatelier's principle?

Answer 30

if a system at equilibrium is subjected to any change the system readjusts itself to counteract the applied change

Question 31

What do we say if the forward reaction is favored?

Answer 31

the equilibrium has shifted to the right

Question 32

What do we say if the reverse reaction is favored?

Answer 32

the equilibrium has shifted to the left

Question 33

What things can be changed to shift the position of equilibrium?

Answer 33

- concentration - temperature - pressure

Question 34

What happens to the position of equilibrium if we increase the concentration on the products and reactants?

Answer 34

INCREASE REACTANTS- favor forward reaction & products INCREASE PRODUCTS- favor reverse reaction & reactants

Question 35

What happens to the position of equilibrium if we decrease the concentration on the products and reactants?

Answer 35

DECREASE REACTANTS- favor reverse reaction & reactants DECREASE PRODUCTS- favor forward reaction & products

Question 36

What happens to the position of equilibrium if we increase and decrease the temperature?

Answer 36

INCREASE- favors endothermic reaction (+ve) DECREASE- favors exothermic reaction (-ve)

Question 37

What happens to the position of the equilibrium if we increase and decrease pressure?

Answer 37

INCREASE- favors side with least GASEOUS moles DECREASE- favors side with most GASEOUS moles

Question 38

What happens to the position of equilibrium if we add a catalyst?

Answer 38

NOTHING- a catalyst speeds up the forward and reverse reaction at the same rate, no overall change. IF A QUESTION ASKS WHAT HAPPENS TO THE FORWARD/REVERSE REACTION IT INCREASES

Question 39

When will pressure not change the position of the equilibrium?

Answer 39

when there's an equal number of gaseous moles on each side

Question 40

What is a standard solution?

Answer 40

a solution of an accurately known concentration

Question 41

How can an endpoint of a titration be shown?

Answer 41

by using an indicator

Question 42

How do we accurately measure solutions in a titration?

Answer 42

by using a pipette

Question 43

Why are titration's used?

Answer 43

to determine unknown concentration