3.1.4 Energetics Flashcards
how is enthalpy change represented
delta H
define enthalpy change
heat energy transferred in a reaction at constant pressure
units for enthalpy change
kJ mol-1
what does delta H with the tube symbol mean
the reactants and products where in there standard states and that the measurements were made under standard conditions
what are standard conditions
100kPa (around 1atm) pressure and a stated temperature
what is a common stated temperature used
298K / 25 degrees Celsius
what does it mean if enthalpy change includes an r
enthalpy change is for a reaction
what does it mean if enthalpy change includes a c
enthalpy change is for combustion
what does it mean if enthalpy change includes an f
enthalpy change is for formation of a new compound
exothermic reactions
give out energy to their surroundings so temperature in the reaction usually goes up
enthalpy change for exothermic reactions
delta H value is negative
why is the delta H value for exothermic reactions negative
products of the reaction end up with less energy than the reactants
is oxidation usually exothermic or endothermic
exothermic
endothermic reactions
endothermic reactions take in energy from their surroundings, so the temperature in the reaction usually falls
enthalpy change for endothermic reactions
delta H is positive
why is delta H value for endothermic reactions positive
products of the reaction have more energy than the reactants
what are bond enthalpies
bond enthalpy is the energy needed to break a bond
is bond breaking exothermic or endothermic
bond breaking is endothermic as you need energy to break bonds
is bond making exothermic or endothermic
bond making is exothermic as energy is released when bonds are formed
does energy required to break a certain bond change
energy required to break a certain type of bond can change depending on where it is
what avg do you use for bond enthalpies in calculations
in calculations you use mean bond enthalpy
what is mean bond enthalpy
average energy needed to break a certain type of bond, over a range of compounds
when is energy absorbed (in bonds)
energy is absorbed to break bonds
when is energy released (in bonds)
energy is released to form bonds
how to calculate enthalpy change of a reaction
enthalpy change of a reaction:
total energy absorbed -
total energy released
define standard enthalpy change of formation
enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
define standard enthalpy change of combustion
enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states
define standard enthalpy change of a reaction
enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all reactants and products in their standard states
