Energetics 🤨 Flashcards
Enthalpy change (kJ mol^-1)
Definitions
The heat energy transferred in a reaction at a constant pressure
Bond enthalpy
Energy required to break bonds
Standard enthalpy of formation
The enthalpy change when 1 mole of a compound is formed from its elements with all substances in their standard states in standard conditions
Standard enthalpy of combustion
The enthalpy change when 1mole of substance is completely burned in oxygen under standard conditions
State Hess’ law
The total enthalpy change of a reaction is independent of the route taken
What are standard conditions
- 100KPa
- 298 K
What are Endothermic reactions
Reactions that Absorb energy from surroundings
What are exothermic reactions
Release energy to surroundings
When bonds are broken what happens to energy
Energy is absorbs when bonds are broken
When bonds are made what happens to energy
Energy is released
Enthalpy change using bond enthalpy equation
Total energy to break bonds- Total energy released forming bonds
You don’t always have to know what to do next; just live.
Give one reason why the bond enthalpy that you calculated is different from the mean bond enthalpy quoted in the data book
Data book value derived from different compounds
A data book value for enthalpy of rea took is -310 Why is there a large difference between the students experimental value and the data book value
Heat loss
How can a student get a more accurate value for enthalpy of reaction
Insulate beaker to reduce heat loss
Record temperature for a suitable time before adding metal to establish an accurate initial temperature
Extrapolate the cooling back to the point of addition to establish a theoretical maximum temperature
