energetics Flashcards
what does system mean in a chem reaction
the atoms and bonds involved in the chem reaction
what does system mean in a chem reaction
the atoms and bonds involved in the chem reaction
law of conservation
amount of energy in an isolated system remains the same.
energy cannot be destroyed or created.
can only be transferred from one form to another
what energy change is breaking bonds associated with
endothermic- energy is taken in
what energy change is making bonds associated with
exothermic- energy is released to make bonds
activation energy
minimum energy required for a reaction to take place
standard T
298K
20 *C
standard P
100kPa
define enthalpy (H)
total energy contents of the reacting materials
define enthalpy change
describe energy exchange that takes place with surroundings under standard conditions
unit of enthalpy change
kJmol
exothermic
energy released on bond formation in the products is greater than absorbed by breaking the bonds in reactants
examples of exothermic reactions
combustion
neutralisation
metal displacement
endothermic
energy needed to be absorbed to break bonds in the reactants is greater than the energy transferred to surroundings as bonds are made in products
examples of endothermic
photosynthesis
thermal decomposition
cracking
4 types of standard enthalpy change
reaction
formation
combustion
neutralisation
define reaction standard enthalpy change
energy transferred when the molar quantities of reactants react under standard conditions
define formation standard enthalpy change
1 mol of a product is formed from its elements under standard states and conditions
example of formation SEC
H2 + 1/2 O2 -> H2O(l)
what is the enthalpy change of a formation of an element always
0 kJmol
define combustion standard enthalpy change
one mol of a substance burns completely in oxygen under standard conditions. must only be one mol of the fuel/reactant.
is combustion endothermic or exothermic
exothermic
is combustion endothermic or exothermic
exothermic
which type of standard enthalpy change always produces one mol of product
formation
which type of standard enthalpy change always uses 1 mol of reactant
combustion
which type of standard enthalpy change always uses 1 mol of reactant
combustion
which type of standard enthalpy change always produces one mol of water
neutralisation
define neutralisation standard enthalpy change
energy change when acid and alkali in an equation for reaction neutralise eachother under standard conditions to form one mol of water
what is the standard enthalpy change of neutralisation if a strong acid is used
-57 kJmol
what is the standard enthalpy change of neutralisation if a weak acid is used
-55/56 kJmol
what is the symbol for standard enthalpy change of neutralisation
△ₙH⦵
what is the symbol for standard enthalpy change of formation
△ᶠH⦵
what is the symbol for standard enthalpy change of combustion
△ᶜH⦵
what is the symbol for standard enthalpy change of reaction
△ᵣH⦵
equation to find amount of energy (q), step 1 in calculating enthalpy change
q=mc△T
equation to find enthalpy change △H
△H=q/n
what assumption do we make when using q=mc△T
we assume that 4.18 (SHC of water) is the SHC of a solution
