Enthalpy Flashcards
define: enthalpy (H)
enthalpy is the heat content that is stored in a chemical reaction.
define: exothermic
exothermic refers to a reaction where the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. (ΔH=negative)
define: endothermic
endothermic refers to a reactions where the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings. (ΔH=positive)
an enthalpy profile is…
a diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
(make sure you can draw these!)
activation energy is..
the minimum energy required to start a reaction (by the breaking of bonds)
what are standard conditions?
pressure: 100kPa (1 atmosphere)
temperature: 298k (25°C)
(and 1.0 mol dm-3 solutions, where solutions are involved)
standard state is…
the physical state of a substance under the standard conditions.
define: the standard enthalpy of reaction
the enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation, under standard conditions.
define: the standard enthalpy of neutralisation
the enthalpy change when 1 mole of water is formed from a reaction between an acid and an alkali, under standard conditions.
define: the standard enthalpy change of combustion
The enthalpy change when one mole of a substance reacts completely with oxygen under standard conditions
define: the standard enthalpy change of formation
The enthalpy change when one mole of a compound is formed from its constituent elements in their standard states.
define: Specific Heat Capacity, (c)
the amount of energy required to raise the temperature of 1g of a substance by 1°C
equation in which enthalpy change can be calculated:
Q=mcΔT
define: bond enthalpy
the enthalpy change that takes place when breaking, by homolytic fission, one mole of a given type of bond in gaseous molecules
what is average bond enthalpy?
the average enthalpy change when breaking, by homolytic fission, one mole of a given type of bond in gaseous molecules
is bond breaking exothermic or endothermic?
endothermic (it requires energy)
is bond making exothermic or endothermic?
exothermic (it releases energy)
what does Hess’ Law state?
if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route
an enthalpy cycle is…
a diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other know enthalpy changes using Hess’ Law.
