Chemical Energetics Flashcards
Define enthalpy change.
The enthalpy change of a reaction is the heat change in a reaction at constant pressure. Symbol for enthalpy is delta H and the unit is kJ.mol-1
What are the standard conditions for enthalpy change?
Temperature: 298 K (25 degrees C)
Pressure: 101 kPa
Describe the energy of bond breaking.
To break a bond, energy needs to be absorbed. Bonds are broken in the reactants. This process is endothermic. Delta H is positive.
If more energy is absorbed when bonds break than is released when new bonds form, the reaction will be endothermic.
Describe the energy of bond making.
When bonds are formed, energy is released. Bonds are formed in the products. This process is exothermic. Delta H is negative.
If more energy is released when new bonds formed than is absorbed when bonds break, the reaction will be exothermic.
Define bond enthalpy.
The amount of energy needed to break 1 mole of a bond type in a molecule in the gaseous state.
Define activation energy.
Minimum amount of energy required for a reaction to occur.
Define standard enthalpy change of reaction.
The enthalpy change of a reaction according to the molar quantities in the equation under standard conditions.
Define standard enthalpy change of neutralisation.
The enthalpy change when an acid and alkali react to form 1 mole of water, under standard conditions
Define standard enthalpy change of formation.
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions.
Define standard enthalpy change of combustion.
The enthalpy change when 1 mole of a substance is completely burned in oxygen to make CO2 and H2O, under standard conditions.
What is the equation for energetic calculations?
Q = m . c . Delta T
What is the equation for enthalpy change from the energetic calculation equation?
Delta H = -Q / n
Define Calorimetry.
Used to work out the enthalpy change of combustion.
