thermochemistry Flashcards
characteristics of exothermic reaction
- releases thermal energy into environment
- surrounding environment becomes hotter
- chemical energy converts to thermal energy
characteristics of endothermic reaction
- absorbs thermal energy from environment
- surrounding environment becomes colder
- thermal energy into chemical energy
do substances become hotter during endothermic reactions?
no, despite absorbing energy, the substance it self doesnt get hotter, but the system/substance gets colder
enthalpy change of exothermic reactions
negative
enthalpy change of endothermic reactions
positive
must energy be released or inputted to break chemical bonds?
energy must be inputted, which is labelled as the activation energy, whereas energy is released when new bonds are formed
define activation energy
the minimum amount of energy required for a chemical reaction to occur (KJ/mol)
is higher or lower activation energy more likely to undergo a chemical reaction in nature
lower activation energy due to less energy required to be inputted, hence easily causing a reaction.
reverse reactions
- sign of delta H flips
- activation energy changes
define combustion reactions
the process in which a substance reacts with O2
characteristics of complete combustion reactions
- produces co2
- more oxygen is used overall
characteristics of incomplete combustion
- produces C (soot/s) or CO(g)
- less oxygen is used overall
differences between complete and incomplete combustion
- products formed
-complete requires more oxygen whereas incomplete uses less oxygen - the delta H value of complete combustion reactions are known whereas incomplete reactions are known.
can fuels be combusted under water?
it is difficult to combust a fuel under water as fuels states are never aqueous.
define partially oxidised
some fuels already have oxygen within them such as propanol and ethanol, hence requires less energy to combust them, hence releases less energy.
characteristics of thermochemical energy
- must have delta h/ heat of combustion on right side , don’t forget negative or positive sign and units
-state of water is liquid as it is always conducted in SLC - delta h can’t be derived from data booklet for incomplete combustion
what happens when there are more amounts of reactants?
when there are double to triple the amount of reactants in an equation, the energy produced also doubles or triples
