energetics Flashcards
what is the definition of enthalpy change?
the energy change per mole under constant pressure
what is the definition of enthalpy change of combustion?
the enthalpy change when one mole of a substance is completely burned in oxygen
what is the definition of enthalpy change of formation?
the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states
what are the standard conditions for enthalpy change?
298K and 100kPa
what is Hess’ law?
total enthalpy change for a process is independent of the root taken
Hess’ law for ΔH formation
ΔH = ΔHf products - ΔHf reactants
Hess’ law for ΔH combustion
ΔH = ΔHc reactants - ΔHc products
when is a reaction exothermic?
when the energy released from the bonds being made is greater than the energy taken in from the bonds being broken
what is bond enthalpy?
the enthalpy change when one mole of covalent bonds in the gaseous state are completely broken
what equation links energy, temperature, specific heat capacity and mass of water together?
q = m x c x ΔT
what equation links enthalpy change, moles and energy together?
ΔH = q / moles reacted
why are calorimetry experiment calculations often lower than theoretical values?
heat loss to the surroundings, evaporation of fuels, incomplete combustion of fuels
how could you improve the accuracy of calorimetry experiments due to heat loss?
better insulation, heat shield for fuels
how should temperature change for a calorimetry experiment for an aqueous reaction by calculated?
measure the start temperature every minute for 4 minutes, mix reactants, record temperature every minute for 4 minutes, plot a graph and regress line of temperature change to find ΔT
