energetics Flashcards
what is enthalpy change?
change in heat energy of a substance under constant pressure
what does an exothermic reaction do?
release energy into the surroundings
what does an endothermic reaction do?
take in energy from the surroundings
what does a +ve deltaH value mean?
the reaction is endothermic
what does a -ve deltaH value mean?
the reaction is exothermic
at what conditions does a standard enthalpy change occur?
100KPa
298K
what is the standard enthalpy of combustion?
the enthalpy change under standard conditions when 1 mole of a substance is burned completely in excess oxygen, with all reactants and products in their standard state
what is the standard enthalpy of formation?
the enthalpy change under standard conditions when 1 mole of a compound is formed from its elements, with all reactants and products in their standard state
what is calorimetry used for?
measuring the heat energy change in a reaction
what is the equation to calculate the energy required (q)?
q = m x c x deltaT
what are errors in calorimetry mainly due to?
heat loss to the surroundings
how can we prevent heat loss in a calorimetry experiment?
use insulating materials
what does hess’ law state?
the enthalpy change of a reaction is independent of the route taken
what is the equation for deltaH of formation
deltaH = sum of products + sum of reactants
what is the equation for deltaH of combustion?
deltaH = sum of reactants - sum of products
what is bond enthalpy?
enthalpy change to break one mole of covalent bonds in gaseous state
deltaH will be positive
what is equation for deltaH of bond enthalpy?
bonds broken - bonds made
what is the equation to find the enthalpy change per mole of a substance?
deltaH = q / molesx10000
