TOPIC 8: Chemical energies Flashcards
What is an exothermic reaction?
Where heat energy is transferred from the system to the surroundings.
What is an exothermic reaction?
Where heat energy is transferred from the surroundings to the system.
What are the exact standard conditions?
- 100KPa (100,000 Pa)
- 298K
What happens under standard conditions?
Standard enthalpy change can occur.
What is the definition of standard enthalpy change of a reaction?
The enthalpy change measured at 100KPa and a stated temperature, usually 298K, when the number of moles of a substance in the equation as written react.
What is the equation to calculate the standard enthalpy change of combustion?
Q=mc△t
Q = Energy
m = Mass
c = Specific heat capacity
△t = Temperature change
What is the definition of standard enthalpy change of combustion?
The enthalpy change measured at 100KPa and a stated temperature, usually 298K, when one mole of a substance is completely burned in oxygen.
What is the definition of standard enthalpy change of neutralization?
The enthalpy change measured at 100KPa and a stated temperature, usually 298K, when one mol of water is produced by the neutralization of an acid with an alkali.
What is the definition of standard enthalpy change of formation?
The enthalpy change measured at 100KPa and a stated temperature, usually 298K, when one mol of a substance is formed from its elements in their standard states.
What is Hess’ Law?
It states that the enthalpy change of a reaction is independent of the path taken in converting reactants to products, provided the initial and final conditions are the same in each case.
How does the Hess’ Law cycle look for combustion?
Combustion is breaking down so arrows pointing down.
How does the Hess’ Law cycle look for formation?
Combustion is building up so arrows pointing up.
What is bond enthalpy?
The enthalpy change when one mole of a bond in its gaseous state is broken.
What is mean bond enthalpy?
The enthalpy change when one mole of a bond, averaged out over many different molecules, is broken.
How to calculate enthalpy change using mean bond enthalpy?
- Calculate the sum of the mean bond enthalpies of the broken bonds.
- Calculate the sum of the mean bond enthalpies of the bonds made.
- Calculate enthalpy change of reaction by using the equation △Enthalpy = Bonds Broken - Bonds Made.
- -ve enthalpy change is exothermic while +ve enthalpy change is endothermic.
