Chapter 16 - speed of reactions

Question 1

what are the four factors that affect the speed of reactions

Answer 1

• particle size
• temperature
• concentration
• pressure

Question 2

explanation for higher speed of reaction - particle size

Answer 2

smaller particle size means larger total surface area. Therefore reactants particles have increased frequency of effective collisions resulting in higher speed of reaction

Question 3

explanation for higher speed of reaction - temperature

Answer 3

at higher temperature particles have more average kinetic energy and they move more vigorously. Therefore reactant particles have increased frequency of effective collisions resulting in higher speed of reaction

Question 4

explanation for higher speed of reaction - concentration

Answer 4

at higher concentration reactants have more particles per unit volume . Therefore reactant particles have increased frequency of effective collisions , resulting in higher speed of reaction.

Question 5

explanation for higher speed of reaction - pressure

Answer 5

at higher pressure there is decreased volume and cause particles to be forced closer together. therefore reactant particles have increased frequency of effective collisions resulting in higher speed of reaction

Question 6

what are the two ways to measure speed of reaction

Answer 6

• collecting volume of gas produced
• measuring the mass of reactants after reaction

Question 7

formula to calculate the speed of reaction in set up one (volume of gaseous product)

Answer 7

speed of reaction = increase in volume of gas produced divided by time taken

Question 8

formula to calculate the speed of reaction in set up two (mass of reactants)

Answer 8

seed of reaction = decrease in mass of reactant mixture divided by the time taken

Question 9

graph facts according to the gradient

Answer 9

steeper gradient faster speed of reaction

Question 10

graph facts according to y axis

Answer 10

greater difference in y axis reading means increase in volume of gaseous product or increase in gaseous product lost

Question 11

how to describe a graph for reaction of the first set up (volume of gaseous product)

Answer 11

• as the reaction begins the gradient is steepest as it is the highest rate of reaction / highest speed of reaction
• as reaction proceeds there is a less steep gradient and rate of reaction / speed of reaction decreases
• as reaction s=comes to a stop there is no gradient and only flat line

Question 12

how to describe a graph for reaction of the second set up (mass of reactants)

Answer 12

• as reaction begins the amount of reactant particles are at the maximum causing the highest rate/ speed of reaction therefore there is the steepest gradient

Question 13

explain using colliding particles why rate of reaction decreases as experiment slows

Answer 13

both reactant X and Y are being used up in reaction so there is lesser particles of reactant X and Y causing the reactant particles to have decreased frequency of effective collisions causing a lower rate/ speed of reaction

Question 14

Zn reacts with sulfuric acid, why does the reaction stop

Answer 14

all the Zn have reacted with the sulfuric acid and is all used up

Question 15

Zn reacts with excess sulfuric acid state one observation to indicate that he reaction has stopped

Answer 15

no more effervescence will be observed

Question 16

Zn reacts with excess sulfuric acid, why is there a loss of mass after the reaction

Answer 16

hydrogen gas was produced and escaped to the surroundings

Question 17

given a volume-time graph explain the rate of change as the experiment progresses

Answer 17

• steepest part is the highest rate of reaction because there are more particles available to react in the beginning
  -less steep gradient means the rate of reaction is getting slower as more reactant particles have been used up as reaction progresses. lesser particles left to react therefore slower rate of reaction
• no gradient = no reaction = reaction complete