5.2 - Energetics
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What is an enthalpy change
The enthalpy change of a reaction is the heat energy it releases or absorbs per mole
What is the symbol used for enthalpy change
ΔH
What signs can enthalpy changes have
+ or -
What is the value in an enthalpy change
the number
What is the unit used for enthalpy change
kJ/mol
what tells us whether the reaction absorbs or releases energy
the sign + or -
If the sign is positive (+) has the reaction absorbed or released heat energy
absorbed
If the sign is negative (-) does the reaction absorbed or released heat energy
released
If the sign is positive (+) is the reaction endothermic or exothermic
endothermic
If the sign is negative (-) is the reaction endothermic or exothermic
exothermic
If the reaction has absorbed heat is the sign positive (+) or negative (-)
positive (+)
If the reaction has released heat is the sign positive (+) or negative (-)
negative (-)
If the reaction has absorbed heat is it endothermic or exothermic
endothermic
If the reaction has released heat is it endothermic or exothermic
exothermic
If the reaction is endothermic is its sign positive (+) or negative (-)
positive (+)
If the reaction is exothermic is its sign positive (+) or negative (-)
negative (-)
If the reaction is endothermic has it absorbed or released heat
absorbed
If the reaction is exothermic has it absorbed or released heat
released
What does the value of an enthalpy change show
how much heat energy is absorbed or released
What do the units of an enthalpy change always the same
they are always kJ/mol so that different reactions can be compared easily
what does how much energy a reaction absorbs or releases depend on
it depends on the balance between: - breaking bonds, absorbs energy - making bonds, releases energy
what does breaking bonds do
absorbs energy
what does making bonds do
releases energy
what does an energy level diagram look like for an endothermic
¦ ____products___ ¦ ^ H¦ ¦ ¦ ¦ΔH(+) ¦_____reactants_____¦ ¦