40S Unit 1: Chemical Kinetics

Question 1

define chemical kinetics

Answer 1

the study of the rate of reactions and the factors involved

Question 2

what is a spontaneous reaction?

Answer 2

a reaction that happens without the addition of energy or outside intervention and nothing forces it to occur

Question 3

define activation energy

Answer 3

the energy needed for a reaction to occur

Question 4

how can you make a reaction occur?

Answer 4

1. lower the activation energy by increasing the temperature
2. lower the activation energy by adding a catalyst

Question 5

what are the factors affecting the spontaneity of a reaction?

Answer 5

entropy and enthalpy

Question 6

define entropy

Answer 6

the level of chaos/organization in a system

Question 7

what is the mathematical symbol for entropy

Answer 7

S

Question 8

define enthalpy

Answer 8

the total energy level of a system

Question 9

what is the mathematical system for enthalpy

Answer 9

H

Question 10

define exothermic

Answer 10

the loss of heat energy from a species

Question 11

define endothermic

Answer 11

the gain/addition of heat energy in a species

Question 12

which one is spontaneous, exothermic or endothermic and why?

Answer 12

exothermic reactions are spontaneous because they loose heat energy, reducing their enthalpy level and causing them to be spontaneous

Question 13

how can an endothermic reaction be spontaneous?

Answer 13

endothermic reactions have a higher enthalpy level, so their entropy increase (increase in chaos) has to be higher than their enthalpy increase.

(entropy rise must be greater than enthalpy rise)

Question 14

in an endothermic reaction and graph, is the change in enthalpy (ΔH) positive or negative?

Answer 14

positive

Question 15

in an exothermic reaction and graph, is the enthalpy change (ΔH) positive or negative?

Answer 15

negative

Question 16

state an example of an exothermic reaction

Answer 16

the decomposition of hydrogen peroxide

H2O2(l) → H2O(l) + O2(g)

Question 17

state an example of an endothermic reaction

Answer 17

the reaction between barium hydroxide and ammonium thiocyanate

Ba(OH)2•8H2O(s) + 2NH4SCN(s) → Ba(SCN)2(s) + 10H2O(l) + 2NH3(g)

Question 18

what is the importance of Gibbs Free Energy and what is the equation?

Answer 18

Gibbs Free Energy (G) is used to determine if a reaction will be spontaneous or not

ΔG = ΔH - TΔS

if G is negative, the reaction is spontaneous

Question 19

state 3 ways to measure the rate of reaction

Answer 19

1. measuring the change in gas production using an inverted graduated cylinder in water
2. measuring the concentration of ion production
3. measuring the production of colour using a colourometer

Question 20

what is reaction rate measured in?

Answer 20

M/s or mol/L/s or mol/L•s

Question 21

what is the formula for reaction rate?

Answer 21

r = Δconcentration (M or mol/L) ÷ time (s)

Question 22

on a concentration vs time graph, the magnitude of the curvature if directly related to the ____________ of the species. that means in this reaction 2NO2(g) → 2NO(g) + O2(g), the curvature of O2 is _________ the curvature of NO and NO2

Answer 22

coefficients
half

Question 23

in reactants does concentration increase or decrease overtime?

Answer 23

decrease

Question 24

in products does reactants increase or decrease overtime?

Answer 24

increase

Question 25

how can you find the reaction rate on a concentration vs time graph?

Answer 25

using the slope where m = Δconcentration ÷ Δtime

Question 26

what are the 2 types of slopes and what is the difference?

Answer 26

tangents and secants

tangents find the instantaneous slope at one point while secants find the average slope between two slopes

Question 27

are tangents and slopes always similar? explain

Answer 27

no they are not. for first order reactions the average rate is similar to the instantaneous rate at the halfway point, but for reactions with higher orders, they might be similar over short intervals of time but they differ over longer time intervals.

Question 28

reactions rates for all species in a chemical reaction are _____________ ________________

Answer 28

stoichiometrically proportional

Question 29

state the rate law equation

Answer 29

r = k • [A]^x • [B]^y • [C]^z

Question 30

in the rate law equation, what is ‘k’ measured in?

Answer 30

mol^-n • L^+n / s

n = overall over - 1

Question 31

what does a zero order mean?

Answer 31

the concentration of a species has no effect on the reaction rate

Question 32

what does a first order mean?

Answer 32

a change in the concentration of a species causes a proportional change on the reaction rate

Question 33

what does a second order mean?

Answer 33

a change in the concentration of a species causes a (proportional change)^2 on the reaction rate

Question 34

what is the overall order of reaction

Answer 34

the sum of all the orders within a given reaction

Question 35

state the 5 factors affecting the reaction rate and experiments to explain them

Answer 35

1. concentration - 18M sulfuric acid + sugar is more dramatic than 4M of sulfuric acid + sugar
2. temperature - Alka seltzer lab
3. surface area (only for different physical states)- metal rod vs steel wool
4. nature of reactants - alkali metals + water gets more reactive down the group
5. catalyst - decomposition of H2O2 is faster with MnO2 which produces ‘elephants toothpaste’

Question 36

what is the formula for proportional change?

Answer 36

porportional Δ = final ÷ initial

Question 37

how do you find ‘k’ in an experiment?

Answer 37

use Trial 1 values and substitute all known values into rate law equation

Question 38

how is the rate law related to the stoichiometry of the chemical reaction in question?

Answer 38

the stoichiometric proportions within a reaction are equal to the rat proportions between the same species at the exact same time