Energetics Flashcards
What is Enthalpy change measured in?
kilojoules per mole (kJ mol-1)
What happens in an exothermic reaction?
- Heat energy released to surroundings
- Negative enthalpy change
- Surroundings temperature increases
What happens in an endothermic reaction?
- Absorb heat energy from the surroundings
- Positive enthalpy change
- Surroundings temperature decreases
Exothermic reaction example?
Combustion
Endothermic reaction example?
Thermal decomposition
What is the activation energy?
Minimum energy needed for a reaction to occur
Exothermic energy levels of reactants and products?
Reactants at a higher energy level than products
Endothermic energy levels of reactants and products?
Reactants at a lower energy level than products
Are substances more or less stable if they have less enthalpy?
They are more stable when they have less enthalpy.
What are the general standard conditions?
298K temperature
101 kPa pressure
What does the standard state of a substance refer to?
Its physical state under standard conditions.
What is the standard enthalpy change of reaction?
The enthalpy when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions.
What is the standard enthalpy change of formation?
Enthalpy change when one mole of a compound forms from its elements under standard conditions.
What is the standard enthalpy change of combustion?
Enthalpy change when 1 mole of a substance combusts fully in oxygen under standard conditions
What is the standard enthalpy change of neutralisation?
Enthalpy change when an acid and alkali neutralise under standard conditions, to form 1 mole of water
What is combustion calorimetry?
Used to find the enthalpy change when a fuel is burned (i.e enthalpy change of combustion)
What is solution calorimetry?
To find the enthalpy changes occurring in an aqueous solution (i.e enthalpy change of neutraliusation)
What is the first law of thermodynamics?
Energy can’t be created or destroyed, only converted from one form to another.
What does Hess’s law state?
The enthalpy change for a reaction is the same, regardless of what route is taken to get from the reactants to the products.
What do chemical reactions involve?
Making and breaking bonds
What is the definition of temperature?
A measure of the average kinetic energy of particles in a system. The faster particles move, the greater their kinetic energy, the higher the temperature.
What is the definition of heat?
A measure of the total energy of all particles in a given amount of any substance.
What does the amount of given out/ taken in by a reaction depend on?
The quantities of the reactants used.
