Thermochemistry 2 ( lesson 4 - 6)

Question 1

Because of the law of conservation of energy, the heat of reaction is the ____ whether the reactants are converted to the products in a ______ ________ or in a ______ of reactions

Answer 1

1. same
   single reaction
   series

Question 2

G.H Hess (1840) suggested that if two or more ______________ _________ are added to give a final equation then the enthalpies can be _____ to give the _______ for the _____ equation

Answer 2

thermochemical equations
added
enthalpy
final

Question 3

Sometimes the heat of reaction for a chemical change is not easily measured due to ____ of reaction, ____, ______ of reactants etc. so we use Hess’s Law to calculate ΔᵣH

Answer 3

time
cost
rarity

Question 4

Hess figured out that the only thing to worry about when finding change in enthalpy is what it was before and what is after______________________________________________

Answer 4

It doesn’t matter what happened in between

Question 5

Sometimes it is not easy to mesaure the heat change for a reaction (too slow/expensive). In this case, ΔH can be determined using ____________________________

Answer 5

heats of formation

Question 6

Heats of formation (_) are the changes in Eₚ that occur when ______________________________

Answer 6

ғH°
compounds are formed from their elements

Question 7

Standard molar enthalpy of formation - the amount of energy change when ___ mole of the compound is made from its elements as they exist at ____

Answer 7

one
SATP

Question 8

ғH° for elements cannot be directly measured, therefore they are designated as ____.. all other ғH° values are in reference to this.. see pages 4-5 in data booklet.

Answer 8

zero

Question 9

The ғH° is an indirect measure of the _________ of a compound

Answer 9

stability

Question 10

The more __________ the formation, the more ______ the compound. (This means you have to ___ that energy to decompose it.)

Answer 10

exothermic
stable
add

Question 11

Hess’s law formula states that ___ is the difference between the standard heats of formation of the _________ and ________

Answer 11

ΔᵣH
reactants
products

Question 12

Take the _______ ________ during the formation of the products and subtract the ______ _____ of the system (energy released when the reactants were formed)

Answer 12

energy released
initial energy

Question 13

Bond energy is the energy _____________________________________ or the energy ____________________________

Answer 13

required to break a chemical bond
released when a bond is formed

Question 14

The _____________________ of a reaction represents the ______________ from ________ the bonds in the reactant(s) and _______ the bonds of the product(s)

Answer 14

change in enthalpy
net effect
breaking
forming

Question 15

In exothermic reactions, bond breaking absorbs _____ energy than the bond formation gives off, resulting in a ___

Answer 15

less
-ΔH

Question 16

In endothermic reactions, bond breaking absorbd ____ energy than the bond formation gives off, resulting in a ___

Answer 16

more
+ΔH

Question 17

The energy barrier that must be overcome for a chemical reaction to occur is called the ________________________

Answer 17

activation energy

Question 18

The atoms in the _________have to be ___________________ in order for them to bond in a different configuration and become the products

Answer 18

reactants
“pulled apart”

Question 19

the activation energy is always ______ than the energy contained in the reactants and products, however the amount of activation energy necessary is dependent on the reaction

Answer 19

higher

Question 20

The ___ of the activation energy barrier on a potential energy diagram represents the ______________________ of a reaction

Answer 20

top
changeover point

Question 21

In both endothermic and exothermic reactions, the molecules of the reactants are moving with a certain amount of ______________

Answer 21

kinetic energy

Question 22

When the reactants _______ with each other, the kinetic energy is transformed into _________________

Answer 22

collide
potential energy

Question 23

This potential energy is then stored in bonds of the chemical species that exists at the top which is called the _______________

Answer 23

activated complex

Question 24

This is a transitional species that is neither a reactant nor a product which has ________________ and is __________________

Answer 24

partial bonds
highly unstable

Question 25

When the patrial bonds of the activated complex re-form as chemical bonds in the products, the stored potential energy is converted back into _______________ as the product molecules ____________

Answer 25

kinetic energy
move apart

Question 26

Rate of reaction meaning

Answer 26

How fast a reaction occurs

Question 27

How to increase the rate of reaction?

Answer 27

• increase temperature
• add catalyst
• increase concentration (or SA + contact)
• increase pressure by decreasing volume (gas)
  - (there is not change in reaction rate if pressure is increased by adding an inert gas)

Question 28

How to increase the rate of reaction?

Answer 28

• increase temperature
• add catalyst
• increase concentration (or SA + contact)
• increase pressure by decreasing volume (gas)
  - (there is no change in reaction rate if pressure is increased by adding an inert gas)

Question 29

A catalyst is a substance that ___________________ of a chemical reaction _____________________ by the reaction

Answer 29

increases the rate
without being consumed

Question 30

catalysts provide _______________ for chemical reactions

Answer 30

alternate pathways

Question 31

They _____ the ________________ required for a reaction to take place which results in the production of a ______________ of products in a given length of time (even at a lower temperature)

Answer 31

lower
activation energy
greater yield

Question 32

In cars we have ______________ that use Pt(s), Pd(s) and Rh(s) to speed up the combustion of exhaust gases so that more of the products are ________ (N₂ instead of NOₓ, CO₂ instead of CO)

Answer 32

catalytic converters
harmless

Question 33

The oil and gas industry uses catalyst (Pt(s), HF(aq), H₂SO₄,(aq) etc) in the ____________ of crude oil and bitumen to make more marketable fuels like gasoline

Answer 33

cracking and reforming

Question 34

compounds that act as catalysts in living systems are called _______
called __________ catalysts eg) amylase, peptidase, lactase

Answer 34

enzymes
biological

Question 35

chemical reactions in the body occur at a very ___ temperature ___ and without catalysts many would be too ____

Answer 35

low
37°C
slow

Question 36

In potential enegery diagrams with an activated complex, what are the features?

Answer 36

Title
reaction progress on x-axis
Ep (potential energy in KJ) on y-axis
activated energy (Ea) from the reactant line to peak of the graph
enthalpy change (difference between reactants and products (could be -ΔH or +ΔH)
Activated complex on peak of graph

Question 37

When a catalyst is used, the activation energy ________ and at the end of the reaction the catalyst is ______

Answer 37

decreases in both the forward and reverse directions
is regenerated

Question 38

What does the formula for heats/enthalpies of formation look like? (draw it)

Answer 38

Question 39

Draw the diagram for the exothermic reaction of The formation of Hydrogen Chloride

Answer 39

In exothermic reactions, bond breaking absorbs less energy than the bond formation gives off, resulting in a -ΔH

Question 40

Draw the diagram for the endo thermic reaction of the decomposition of water.

Answer 40

Question 41

Draw the Potential Energy Diagram for an exothermic reaction with activation energy

Answer 41