Thermochemistry 2 ( lesson 4 - 6) Flashcards
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
- same
single reaction
series
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
thermochemical equations
added
enthalpy
final
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
time
cost
rarity
Hess figured out that the only thing to worry about when finding change in enthalpy is what it was before and what is after______________________________________________
It doesn’t matter what happened in between
Sometimes it is not easy to mesaure the heat change for a reaction (too slow/expensive). In this case, ΔH can be determined using ____________________________
heats of formation
Heats of formation (_) are the changes in Eₚ that occur when ______________________________
ғH°
compounds are formed from their elements
Standard molar enthalpy of formation - the amount of energy change when ___ mole of the compound is made from its elements as they exist at ____
one
SATP
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.
zero
The ғH° is an indirect measure of the _________ of a compound
stability
The more __________ the formation, the more ______ the compound. (This means you have to ___ that energy to decompose it.)
exothermic
stable
add
Hess’s law formula states that ___ is the difference between the standard heats of formation of the _________ and ________
ΔᵣH
reactants
products
Take the _______ ________ during the formation of the products and subtract the ______ _____ of the system (energy released when the reactants were formed)
energy released
initial energy
Bond energy is the energy _____________________________________ or the energy ____________________________
required to break a chemical bond
released when a bond is formed
The _____________________ of a reaction represents the ______________ from ________ the bonds in the reactant(s) and _______ the bonds of the product(s)
change in enthalpy
net effect
breaking
forming
In exothermic reactions, bond breaking absorbs _____ energy than the bond formation gives off, resulting in a ___
less
-ΔH
In endothermic reactions, bond breaking absorbd ____ energy than the bond formation gives off, resulting in a ___
more
+ΔH
The energy barrier that must be overcome for a chemical reaction to occur is called the ________________________
activation energy
The atoms in the _________have to be ___________________ in order for them to bond in a different configuration and become the products
reactants
“pulled apart”
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
higher
The ___ of the activation energy barrier on a potential energy diagram represents the ______________________ of a reaction
top
changeover point
In both endothermic and exothermic reactions, the molecules of the reactants are moving with a certain amount of ______________
kinetic energy
When the reactants _______ with each other, the kinetic energy is transformed into _________________
collide
potential energy
This potential energy is then stored in bonds of the chemical species that exists at the top which is called the _______________
activated complex
This is a transitional species that is neither a reactant nor a product which has ________________ and is __________________
partial bonds
highly unstable
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
Rate of reaction meaning
How fast a reaction occurs
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)
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)
A catalyst is a substance that ___________________ of a chemical reaction _____________________ by the reaction
increases the rate
without being consumed
catalysts provide _______________ for chemical reactions
alternate pathways
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
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
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
compounds that act as catalysts in living systems are called _______
called __________ catalysts eg) amylase, peptidase, lactase
enzymes
biological
chemical reactions in the body occur at a very ___ temperature ___ and without catalysts many would be too ____
low
37°C
slow
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
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
What does the formula for heats/enthalpies of formation look like? (draw it)
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
Draw the diagram for the endo thermic reaction of the decomposition of water.
Draw the Potential Energy Diagram for an exothermic reaction with activation energy
