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chemistry
energy changes-unit5
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Cards (26)
Why can't energy be created or destroyed in reactions?
Because
energy is
conserved
in reactions
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What happens to the amount of energy in the universe?
It always stays the same as can’t be created or destroyed
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What is an exothermic reaction?
A reaction that transfers energy to
surroundings
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How is an exothermic reaction indicated?
By a rise in
temperature
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Why is combustion considered exothermic?
It gives out a lot of
energy
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What type of reaction is neutralization?
Exothermic
reaction
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What happens in many oxidation reactions?
They are
exothermic
and release energy
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What happens when sodium is added to water?
It releases energy and moves on surface of water as is oxidised
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What is a common use of exothermic reactions?
Hand warmers using
iron oxidation
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How do self-heating cans work?
They rely on
exothermic
reactions in
bases
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What is an endothermic reaction?
A reaction that takes in energy from
surroundings
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How is an endothermic reaction indicated?
By a fall in
temperature
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Are endothermic reactions common or rare?
They are much less common than
exothermic
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What happens during thermal decomposition of calcium carbonate?
It decomposes into
calcium oxide
and
carbon dioxide
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What is produced when calcium carbonate decomposes?
Calcium oxide
(
quicklime
) and carbon dioxide
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How are endothermic reactions used in sports injury packs?
They cool the pack
instantly
without refrigeration
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What are the key differences between exothermic and endothermic reactions?
Exothermic reactions release energy; endothermic reactions absorb energy.
Exothermic reactions show a rise in
temperature
; endothermic reactions show a fall in temperature.
Exothermic reactions are more common than endothermic reactions.
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what do réaction profiles show
-relative energies of
reactants
and
products
-how energy changes over the
course
of the reaction
which is at a lower energy in an exothermic reaction
the
products
are lower than the
reactants
what does the difference in height of the products and reactants show on an energy profile
overall energy change
what is the difference in height between the reactants and the highest point on the graph in a reaction profile
activation energy
what is activation energy
the
minimum
amount of energy needed to start the reaction
which is at the lower point for an endothermic reaction profile
reactants
is lower than
products
what happens to the bonds during chemical reactions
old
bonds are
broken
and
new
bonds are
formed
is bond breaking exothermic or endothermic
endothermic
, energy supplied to break existing bonds
is bond formation exothermic or endothermic
exothermic
,
energy
released when new bons are
formed