Energetics, Enthalpy and stuff. Flashcards
Define Exothermic reaction.
Exothermic reactions is a type of reaction where energy is released to the surrounding. /\H is NEGATIVE.
Define Endothermic reaction.
Endothermic reaction is a type of reaction where energy is absorbed from the surroundings. /\H is POSITIVE.
Making and breaking bonds in terms of energy.
Making bonds releases energy, it is an exothermic process.
Breaking bonds requires energy to be supplied, it is an endothermic process.
How do you count the energy value(/\H) in a reaction having bond enthalpies?
The difference between overall energy required to form bonds and to break them.
Therefore - if an energy released from forming bonds is greater than energy needed to break them - the reaction is exothermic; If energy absorbed from the surrounding when breaking bonds is greater than energy released - the reaction is endothermic.
Are bond energies in data booklets exact?
No, these are averages. Same bonds might need different energies depending on the conditions.
How does bond length impact the strength of the bond? Include double and triple bonds.
The shorter the length - the stronger the bond and therefore takes more energy to break.
Double and triple bonds are shorter and stronger than single bonds.
Standard conditions:
Room temperature - 25°C, 298°K
Pressure - 1 atmospheric pressure (101kPa)
Concentration - 1 moldm^-3
Standard state of the substance.
Define Standard enthalpy of combustion:
Standard enthalpy of combustion /\cH - enthalpy change when 1 mole of a substance is combusted in an excess oxygen under standard conditions.
Define Standard enthalpy of formation:
Standard enthalpy of formation /\fH - enthalpy change when 1 mole of a substance is formed from its original elements in their original states under standard conditions.
Define Standard enthalpy of neutralisation*:
Standard enthalpy of neutralisation /\nH - enthalpy change when 1 mole of a water is formed in a reaction between an alkali and an acid under standard conditions.
Define Standard enthalpy change of reaction(just in case):
The standard enthalpy change of reaction /\rH - enthalpy change for a specific reaction when the reaction quantities react under standard conditions.
Energy change formula, units. (Do some more practice on these I beg you)
- Q = mc/\T
Q - kJ/kJmol^-1
m - mass in g
c - specific heat capacity of water = 4.18 J g^-1 K^-1
/\T - change in temperature - /\H = -mc/\T
Hess’s law!*
The enthalpy change of a reaction is independent of the path taken.
Please do more practice on calculations we both know how important that is.
Yes I know
