Themochemistry Definitions

First Law of Thermodynamics

• law of conservation of energy

• energy cannot be created or destroyed; it only changes form

making a bond

releases energy

breaking a bond

absorbs energy

change in energy within reaction occur when…

old bonds are broken and new bonds form

thermal energy

• kinetic energy of molecules

• proportional to temperature

heat

the transfer of energy typically into thermal energy

system

tiny bit of matter that’s being studied

open system

matter & energy can be transferred

closed system

only energy can move, not matter

isolated system

no matter & no energy can be transferred

a beaker of liquid over a short time

can act like a closed system

surroundings

all matter in the universe that is NOT the system. can often even include the water it is being dissolved in

surroundings

all matter in the universe that is NOT the system. can often even include the water it is being dissolved in

formula for photosynthesis

6CO2 + 6H2O + energy → C6H12O6 + 6O2

exothermic reaction

releases energy to surroundings

endothermic reaction

absorbs energy from surroundings

enthalpy/heat of reaction

• amount of heat released or absorbed in the reaction

• equal to change in potential energy of system

• given the symbol ΔH

enthalpy HΔ of exothermic reaction

negative

enthalpy ΔH of endothermic reaction

positive