Chapter 5. Chemical Energetics Flashcards
What is enthalpy
The total energy associated with reactants or products, symbol H.
What are the signs for enthalpy changes
Enthalpy change is negative for exothermic reactions(bond forming) and positive for endothermic(bond breaking)
What is the formular for calculating enthalpy change
△H = H(products) - H(reactants)
What are the standard conditions
- Temp==>250C
- Pressure ==> 1 atm or 101kPa
3.Concentration of 1M
Define standard enthalpy change of reaction, △Hɵr
The enthalpy change when the amounts of reactants shown in the equation react to give products under standard conditions
Define standard enthalpy change of formation,
△Hɵf
The enthalpy change when one mole of a compound is formed from its elements under standard conditions.
Define standard enthalpy change of combustion, △Hɵc
The enthalpy change of combustion is the enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions
Define standard enthalpy change of neutralization, △Hɵn
The enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard conditions
Define standard enthalpy change of atomization, △Hɵat
The enthalpy change when one mole of gaseous atoms is formed from its elements under standard conditions
What is average bond enthalpy
Average enthalpy change when one mole of a covalent bond is broken in gaseous condition
What is the formula for calculating enthalpy change of reaction from bond energies, enthalpy change of formation and enthalpy change of combustion separately?
1.Bond energies
-bond energies of reactants - bond energies of products
2.Formation
- Hf(products) - Hf(reactants)
3.Combustion
-Hc(reactants) - Hc(products)
What is thermochemistry?
The study of heat changes during chemical reactions.
What exothermic reactions and endothermic reactions?
Exothermic reactions give out heat and endothermic reactions take in heat.
What is enthalpy?
Enthalpy is the total energy associated with reactants or products
What is Hess’ law?
Hess’ law states that ‘the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place as long as the initial and final conditions are the same’.
