energetics Flashcards
define enthalpy change
heat energy change at a constant pressure
state hess’ law
enthalpy change of a reaction
is independent of the route taken from reactants to products
what is bond enthalpy
the energy needed to break a bond
what is mean bond enthalpy
the average energy needed to break a certain type of bond over a range of compounds
what is enthalpy change of formation
enthalpy change when
1mole of compound formed
from elements in standard states
under standard conditions
what is standard enthalpy change of combustion
enthalpy change when
1 mole of substance is completely burnt
in oxygen under standard conditions
with all reactants and products in standard states
what is standard enthalpy change of reaction
enthalpy change when a reaction occurs in molar quantities shown in chemical equation
under standard conditions
all reactants and products in standard states
what does collision theory state
a reaction will only occur when two particles collide if they have: the correct orientation, the activation energy
what is the activation energy of a reaction
the minimum amount of energy particles need to react
what are the labells for the axis on a maxwell boltzman curve
X- energy
Y-number of molecules
what is the affect of increasing temperature on rate of reaction
molecules will have more energy so a greater proportion will have the activation of molecules will have the activation energy
the molecules also have increased speed
increased frequency of collisions and increased amount of successful collisons
what is the affect of increasing concentration on rate of reaction
increases rate of reaction as:
more molecules to collide with each other
as increased frequency of collisions
what is the affect of pressure in a gas on rate of reaction
increased rate of reaction as:
molecules closer together so increased frequency of successful collisions
what is dynamic equilibrium
for a reversible reaction
rate of forward and backwards reactions are equal
can only occur in a closed system
what is le chatelier’s principle
for a reaction at equilbrium if its subjected to a chnage in concentration pressure or temperature the position of the equilibrium wil move to counteract the change
