Chapter 9 - Enthalpy Flashcards
What is the law of conservation of energy?
Energy cannot be created or destroyed
What happens when a chemical reaction involving enthalpy change takes place?
Heat energy is transferred between the system and the surroundings
What is enthalpy?
Is the measure of heat energy present in a chemical system
What is meant by enthalpy change?
Is the amount of energy released/taken in during a chemical reaction
What is meant by a exothermic reaction?
Reaction which releases energy into the surroundings
What is meant by an endothermic reaction?
Reaction which takes in energy from the surroundings
What is meant by activation energy?
Is the minimum energy required for a reaction take place
Draw the enthalpy diagram of an exothermic reaction
Draw the enthalpy diagram of an endothermic reaction
What are the standard conditions?
100kPA
298K
1 mol dm^-3
What is meant by the standard state?
The physical state of a substance under standard conditions
What is the standard enthalpy change of reaction (ΔH°r)?
Is the enthalpy change associated with a stated equation in the molar quantities shown in the chemical equation under standard conditions
What is the standard enthalpy change of formation (ΔH°f)?
Is the enthalpy change associated with the formation of 1 mole of a compound from its elements under standard conditions
What is the standard enthalpy change of combustion (ΔH°c)
Is the enthalpy change associated with the complete combustion of 1 mole of a substance under standard conditions
What is the standard enthalpy change of neutralisation (ΔH°neut)
Is the enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between an acid and a base, under standard conditions
How do we calculate the heat energy transferred?
Q=mc∆t
Mass in grams
Temperature change in Kelvins (Add 273)
The specific heat capacity is usually 4.18 J g⁻¹ K⁻¹ in water
What is meant by the specific heat capacity?
Is the energy required to raise 1g of a substance by 1K
What is a cooling curve?
A cooling curve extrapolation can be used to increase the accuracy of the ∆H value obtained as it corrects for heat loss during the experiment
What is meant by average bond enthalpy?
The energy required to break one mole of a specified type of bond in a gaseous molecule
What is required to break bonds and what type of reaction is it?
Energy
Endothermic
BENDO
∆H is +ve
What is required to make bonds and what type of reaction is it?
Release of energy
Exothermic
MEXO
∆H is -ve
How do we calculate enthalpy changes from average bond enthalpies?
∆rH = Σ(bond enthalpies in reactants) - Σ(bond enthalpies in products)
What is Hess’ Law?
If a reaction can take place by two routes, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route
