unit 1 section 4 energetics Flashcards
what is enthaply change
it is the heat energy transferred in a reaction at constant pressure.
what are the standard conditions ( what is the pressure and the temperature )
pressure 100 Kpa ( 1 atm )
temperature 298K or 25 degrees
what is an exothermic reaction
it is a reaction that gives out energy to its surroundings , the enthaply change is negative.
what is an endothermic reaction
it is a reaction that takes in energy from its surroundings, the enthaply change of the reaction is positive.
what is bond enthaply
it is the amount of energy needed to break a bond.
is breaking bonds exothermic or is it endothermic and is making bonds endothermic or is it exothermic
breaking bonds - endothermic ( energy is taken in
making bonds - exothermic ( energy is released )
what is mean bond enthaply
it is the average energy needed to break a certain type of bond, over a range of compounds.
why do you use the mean bond enthaply
because the amount of energy required to break a certain type of bond changes depending on where it is
how to work out the enthaply change of a reaction when you are only given the mean bond enthaplies
use the equation
enthaply change = BB - BC
bonds broken
bonds created
what is the standard enthaply change of formation
it is the enthaply change when 1 mole of an compound is formed from its constituent elements under standard states and conditions.
what is the standard enthaply change of combustion
it is the enthaply change when 1 mole of a substance is completely burned in oxygen under standard states and conditions.
what equations are used in calorimetry to solve for the enthaply change
Q(in j)=M(in g) C(4.18) ΔT (in kelvin)
q=mcΔt
ΔH = Q (in kj) / n
what is Hess’ law
the total enthaply change of a reaction is independent of route taken
what way do the arrows point in enthaply of formation ( do they point up or down )
the arrows will point up.
which way does the arrows point in enthaply of combustion ( do they point up or do they point down )
the arrows point down.
