REACTIVITY 1

exothermic reaction

• heat is released into the surroundings

• enthalpy is aways negative

• products are more stable than reactants

• making bonds

endothermic reactions

• heat is absorbed from the surroundings

• enthalpy is always positive

• reactants are more stable than products

• breaking bonds

heat

form of energy transfer as a result of temperature difference.

-Q=

nΔH

bond enthalpy

energy required to break one mole of bonds in a gaseous subtance.

Hess’s law

the enthalpy change of a reaction is independent of the path, provided the initial and final states are the same.

enthalpy of formation

the enthalpy change to make one mole of a substance from its elements. at standard conditions

enthalpy of combustion

enthalpy of a subtance when one mole of a substance is burned completely

metals reacting with oxygen

create solids (basic)

non-metals reacting with oxygen

produce gases (acidic)

complete combustion

products are CO2 and water only

incomplete combustion

typically get carbon sut and CO and water

is usually caused by limited oxygen amount

fuels with high % of carbon

fossil fuels

made of the partial decomposition of plant and animal material

non-renewable

significant greenhouse gas producers.

biofuels

fixing carbon through photosynthesis in short periods of time

renewable

carbon neutral:

wood, ethanol, methanol

greenhouse gas

incoming short wave radiation from the sun is absorbed by the earth and re emits the radiation as long waves IR which is absorbed by CO2

Fuel cell

converts chemical energy directly to electrical using a continuous flow of reactants.

pros and cons of hydrogen fuel cell

only require hydrogen and oxygen

not pollutant

entropy

measure of the distribution between particles how disordered the particles are.

spontaneous reaction

a reaction which doesnt require energy to proceed once started

non-spontaneous reaction

reaction which continually requires energy to proceed

factors which favour spontaneous reactions.

lose energy (exothermic)

gain in entropy

when can low enthalpy and low entropy result in a spontanous reaction

at low temperatures

when can high enthalpy and high entropy result in a spontanous reaction

at high temperetures.