Thermochemistry 2 ( lesson 4 - 6) Flashcards

1
Q

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

A
  1. same
    single reaction
    series
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2
Q

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

A

thermochemical equations
added
enthalpy
final

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3
Q

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

A

time
cost
rarity

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4
Q

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

A

It doesn’t matter what happened in between

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5
Q

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

A

heats of formation

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6
Q

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

A

ғH°
compounds are formed from their elements

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7
Q

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

A

one
SATP

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8
Q

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.

A

zero

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9
Q

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

A

stability

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10
Q

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

A

exothermic
stable
add

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11
Q

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

A

ΔᵣH
reactants
products

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12
Q

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

A

energy released
initial energy

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13
Q

Bond energy is the energy _____________________________________ or the energy ____________________________

A

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

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14
Q

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

A

change in enthalpy
net effect
breaking
forming

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15
Q

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

A

less
-ΔH

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16
Q

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

A

more
+ΔH

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17
Q

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

A

activation energy

18
Q

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

A

reactants
“pulled apart”

19
Q

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

20
Q

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

A

top
changeover point

21
Q

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

A

kinetic energy

22
Q

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

A

collide
potential energy

23
Q

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

A

activated complex

24
Q

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

A

partial bonds
highly unstable

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 ____________
kinetic energy move apart
26
Rate of reaction meaning
How fast a reaction occurs
27
How to increase the rate of reaction?
- 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)
28
How to increase the rate of reaction?
- 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)
29
A catalyst is a substance that ___________________ of a chemical reaction _____________________ by the reaction
increases the rate without being consumed
30
catalysts provide _______________ for chemical reactions
alternate pathways
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)
lower activation energy greater yield
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)
catalytic converters harmless
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
cracking and reforming
34
compounds that act as catalysts in living systems are called _______ called __________ catalysts eg) amylase, peptidase, lactase
enzymes biological
35
chemical reactions in the body occur at a very ___ temperature ___ and without catalysts many would be too ____
low 37°C slow
36
In potential enegery diagrams with an activated complex, what are the features?
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
37
When a catalyst is used, the activation energy ________ and at the end of the reaction the catalyst is ______
decreases in both the forward and reverse directions is regenerated
38
What does the formula for heats/enthalpies of formation look like? (draw it)
39
Draw the diagram for the exothermic reaction of The formation of Hydrogen Chloride
In exothermic reactions, bond breaking absorbs less energy than the bond formation gives off, resulting in a -ΔH
40
Draw the diagram for the endo thermic reaction of the decomposition of water.
41
Draw the Potential Energy Diagram for an exothermic reaction with activation energy