Thermochemistry Flashcards
what is thermochemistry?
deals with the change in energy that occurs during a chemical reaction
chemical equations v thermochemical equations
- they are different
- thermochemical must have enthalpy value
what is an enthalpy value?
tell chemist about the reaction participants and about energy change. enthalpy is defined as the amount of energy change per set amount of substance
to use enthalpy in mol what must be present
chemical formula
incomplete combustion
- limited O2
- products CO and H2O
- all product gas
complete combustion
- O2
- products CO2 and H2O
- products gas
how to balance combustion reactions normally?
CHO
how to balance when oxygen is present in the fuel or reactant?
need to subtract O atom total in the products by the number of O atoms in the chemical reactant (not O2) before you balance O2
if you have to halve or double the stoichiometry you must…. the enthalpy
halve or double
how do you reverse a thermochemical equation?
stoich is the same but enthalpy value becomes positive
how does the state of water impact the enthalpy value?
H2O to liquid releases heat
H2O to gas needs heat
what are the thermochemical reaction types?
endothermic or exothermic
endothermic?
- absorb thermal energy from surrounding environment
- prac will indicate a decrease in temp
exothermic?
- release thermal energy to environment
- prac indicates an increase in temp
what is activation energy needed for?
to break bonds