enthalpy changes Flashcards
define enthalpy
the heat content in a system
define enthalpy change
the heat evolved in a system
define endothermic
more energy required to breaks bonds of reactants than energy released when bonds form in products
define exothermic
more energy released when bonds form in products than energy absorbed to break bonds in reactants
what type of reaction is anabolic?
endothermic
what type of reaction is catabolic?
exothermic
define Hess’s law?
if a reaction can take place by more than one route and the starting and finishing conditions are the same, the enthalpy change is the same irrespective of the route
define standard enthalpy change of formation
enthalpy change when one mole of a compound is formed from its constituent elements where both the reactants and product is in standard state in standard conditions of 298K, 1 atm or 100kPa
define enthalpy change of combustion
enthalpy change when one mole of a compound completely burns in oxygen in standard state in standard conditions of 298k and 100kPa
define enthalpy change of neutralisation
enthalpy change when an acid and base react to form one mole of water in standard states and standard conditions of 298K and 100kPa
define enthalpy change of reaction
enthalpy change that accompanies a reactions in its molar quantities shown in the chemical equation in standard states and standard conditions of 298K and 100kPa
why is the less enthalpy change less exothermic than expected?
- heat loss to the surroundings
- incompletes combustion
- not in standard conditions
- evaporation of fuel(be specific of what fuel in the exam) from the wick
when working out enthalpy change of neutralisation, what is an important thing you should do?
- make sure to include the volumes of both the acid and alkali added to work out the mass
