DF1:1 Getting Energy From Fuels Flashcards
What is the enthalpy change of a reaction?
The heat change of a reaction at constant pressure.
What are the units for enthalpy change?
kJ/mol
What is the symbol for enthalpy change?
Delta H ^standard conditions
What are the standard conditions?
100kPa pressure and 298 Kalvin.
How do you work out Kalvin?
Degrees celcius + 273
What happens in an endothermic reaction?
Energy is absorbed from the surroundings.
What happens in an exothermic reaction?
Energy is released to the surroundings.
What does an enthalpy level diagram look like for an exothermic reaction?
The products are lower in energy than the reactants, enthalpy change is negative.
What does an enthalpy level diagram look like for an endothermic reaction?
The products are higher in energy than the reactants, enthalpy change is positive.
What is an example of an exothermic reaction and why?
Combustion, as heat is being lost into the surroundings.
What is an example of an endothermic reaction and why?
Thermal decomposition, as the compound is being broken down by heat and energy is absorbed when bonds are broken.
What is standard enthalpy change of reaction?
The enthalpy change of a reaction according to the molar quantities in the equation under standard conditions.
What is the symbol for standard enthalpy change of reaction?
Delta r H ^standard conditions.
What is standard enthalpy change of neutralisation?
The enthalpy change when an acid and alkali react to form one mole of water under standard conditions.
What is the symbol for standard enthalpy change of neutralisation?
Delta neut H ^standard conditions.
What is 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 symbol for standard enthalpy change of combustion?
Delta c H ^standard conditions.
What is standard enthalpy change of formation?
The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.
What is the symbol for standard enthalpy change of formation?
Delta f H ^standard conditions.
What reaction is breaking bonds?
Endothermic.
What reaction is the forming of bonds?
Exothermic.
What is bond dissociation enthalpy?
The energy needed per mole to break attractive forces in bonds in only gaseous compounds.
Why do we work out the mean bond enthalpy?
Bonds of the same type don’t all have the same amount of energy.
