enthalpy changes Flashcards
what is enthalpy change
the amount of heat energy transferred during a chemical reaction at constant pressure.
what in an energy profile diagram represents that a reaction is exothermic
the products are at lower energy than the reactants (heat is transferred to surroundings)
what are the common examples of exothermic reactions
combustion
respiration (oxidation of glucose)
neutralisation
what in an energy profile represents that a reaction is endothermic
the products are at higher energy than reactants (energy has been transferred to system)
common examples of an endothermic reaction
thermal decomposition
photosynthesis
what is activation energy
the minimum energy required for a reaction to take place by breaking bonds in reactants
where is activation energy and enthalpy change labelled in an energy profile diagram.
activation energy; from reactants to peak.
enthalpy change; from reactants to products
what are the standard conditions for enthalpy change
temp= 298k
pressure=100kPa
all solutions= 1.00mol/dm3
what is standard state of : H20, NaCl, Cl2, O2, NH3, sulfur, iodine, carbon, sulfur dioxide
liquid, solid,gas,gas,gas,solid,solid,soliod,gas (respectively)
standard enthalpy change of a reaction
the enthalpy change for a given reaction in the molar quantities shown in the equation (exothermic or exothermic)
standard enthalpy of combustion
the enthalpy change when 1 mol of a substance completely combusts at 298k and 100KPa. (always exothermic)
standard enthalpy of formation
the enthalpy change when 1 mol of a compound is formed from its elements at 298k and 100KPa (can be either)
what is the value for standard enthalpy of formation and why
0, because there is no change involved
standard enthalpy change of neutralisation
the enthalpy change when 1 mol of H2O is formed from the reaction of H+ and OH- at 298K and 100KPa. (always exothermic) and energy enthalpy is -57
how to calculate energy released in an exothermic reaction
enthalpy change * moles
