T.6 Energetics

Question 1

Define rate

Answer 1

Change (decr) in the concentration of reactant per unit time
OR Change (incr) in the concentration of product per unit time

Rate always positive

Question 2

What properties can be used to determine rate of a reaction?

Answer 2

Color (absorption of colored light)
Electrical conductivity
Volume/mass/pressure of gas

Question 3

What does the gradient of a graph of property vs time tell you?

Answer 3

The gradient is PROPORTIONAL to the rate.

Question 4

What kind of graph do you need to determine rate?

Answer 4

Concentration vs time. Then the gradient (tabgent) = the rate (rate=conc/time)

Question 5

Why does rate of reaction generally decrease with time?

Answer 5

Reactants are used up.
(Smaller change conc reactants and smaller incr conc products)

Question 6

List techniques for measuring rate

Answer 6

Clock technique —- time for particular event to occur, eg color change
Titration (remove small samples at diff times)
Collection of evolved gas/increase in pressure
Measuring mass
Light absorption
Electric conductivity

Question 7

Outline collision theory

Answer 7

For 2 particles to react, they have to collide with the correct geometrical alignment AND have enough energy to overcome the activation energy

Question 8

Define activation energy

Answer 8

The minimum energy for a reaction to occur (must have E equal or greater than Ea)

Question 9

Low Ea vs High Ea in relation to rate.

Answer 9

Low Ea —> fast rate

High Ea —> slow rate

Question 10

Factors affecting the rate of reaction and HOW they affect it