C5 - monitoring and controlling chemical reactions (from PMT)

Question 1

define concentration

Answer 1

the amount/mass of a substance in a given volume of solution

Question 2

what equipment is required for a standard titration?

Answer 2

-burette
-conical flask
-pipette + pipette filler
-white tile
-funnel
-clamp + stand

Question 3

why must the conical flask be swirled during a titration?

Answer 3

to ensure all the particles react

Question 4

define the molar volume of a gas

Answer 4

the volume occupied by one mole of any gas at room temperature and pressure

Question 5

what is the molar volume of gas at room temperature and pressure?

Answer 5

24dm^3 or 24,000cm^3

Question 6

what is RTP?

Answer 6

room temperature + pressure
-20 degrees
-1 atmosphere

Question 7

how can the volume of gas be calculated at RTP?

Answer 7

volume at RTP (dm^3) = moles * 24

Question 8

why is percentage yield usually less than 100%?

Answer 8

-incomplete reaction
-some of the product may have escaped (if gaseous) or vaporised
-impurities in the starting material

Question 9

define atom economy

Answer 9

a measure of how many reactant atoms in a chemical reaction are used to form a desired product

Question 10

how can atom economy be calculated?

Answer 10

atom economy = molecular mass of desired product / total molecular mass of reactants

Question 11

what must be considered when choosing the most appropriate reaction pathway?

Answer 11

-percentage yield
-atom economy
-uses of by-products
-rate of reaction
-position of equilibrium
-availability of reactants

Question 12

how can rate of reaction be calculated?

Answer 12

rate of reaction = atom of product formed or reactant used / time

Question 13

why is the disappearing cross rate of reaction experiment not very accurate?

Answer 13

-it’s very subjective, people might disagree about the exact point the black cross disappears

Question 14

what conditions can be changed to increase the rate of a reaction?

Answer 14

-increase temperature
-increase pressure
-increase surface area of reactants
-increase concentration of reactants

Question 15

how does surface affect the rate of reaction?

Answer 15

increasing surface area increases the rate of reaction because more reacting particles are exposed so there are more frequent successful collisions

Question 16

how does concentration affect the rate of reaction?

Answer 16

increasing concentration increases the rate of reaction because there are more reacting particles in the same volume. this means more frequent successful collisions occur.

Question 17

how does pressure affect the rate of a gaseous reaction?

Answer 17

increasing the pressure of a gaseous reaction increases the rate of reaction because there are more more reacting particles in the same volume of gas so there are more frequent successful collisions

Question 18

what can be added to speed up the rate of a reaction?

Answer 18

catalyst

Question 19

define a catalyst

Answer 19

a substance which speeds up the rate of reaction without being chemically changed at the end

Question 20

how does a catalyst affect the rate of reaction?

Answer 20

a catalyst increases the rate of reaction because it provides an alternate reaction pathway with a lower activation energy. more particles have energy above the activation energy so more frequent successful collisions will occur.

Question 21

how can a catalyst be identified in a reaction?

Answer 21

they are chemically unchanged so can be distinguished from the product. they are not involved in the reaction equation as they are not used up.

Question 22

how can the direction of a reversible reaction be changed?

Answer 22

by changing the conditions

Question 23

what is meant by the term dynamic equilibrium?

Answer 23

dynamic equilibrium occurs in a closed system when the rates of the forward and backward reactions are equal. the concentration of reactants and products remain constant.

Question 24

what is le chatelier’s principle?

Answer 24

if a reaction at equilibrium is subjected to a change in temperature, concentration or pressure, the position of equilibrium will shift to oppose this change.

Question 25

what happens to the position of equilibrium if the concentration of the reactants increases?

Answer 25

the position of equilibrium will shift right (towards the products) to reduce the concentration of reactants and form more products

Question 26

what happens to the position of equilibrium if the concentration of the products increases?

Answer 26

the position of equilibrium will shift left (towards the reactants) to decrease the concentration of products and form more reactants

Question 27

how does a change in pressure affect the position of equilibrium?

Answer 27

increasing the pressure causes the position of equilibrium to shift towards the side with the fewest gaseous moles in order to counteract the pressure change

Question 28

what happens to the position of equilibrium if the temperature of a reaction is increased?

Answer 28

the position of equilibrium shifts in the direction of the endothermic reaction to take in more heat energy from the surroundings