3.1.4.1 Enthalpy change Flashcards
What is enthalpy?
Refers to all of the heat energy that is stored in a chemical system
What is enthalpy change?
The heat (energy) change at constant pressure (deltaH)
What is exothermic change?
In an exothermic change, energy is transferred from the system to the surroundings.
Surrounding temperature: increases
Products have less energy than reactants
What are examples of exothermic reactions?
Combustion, neutralisation
What is an endothermic change?
In an endothermic change, energy is transferred from the surroundings to the system;
surrounding temp.: decreases
Products have more energy than reactants
What are examples of endothermic reactions?
Thermal decomposition of calcium carbonate
How does the reaction profile diagram show that a reaction is exothermic/ endothermic?
Exo: energy of products is smaller than the energy of the reactants
Endo: energy of reactants is smaller than the energy of products
What is standard enthalpy change and what are the conditions?
Enthalpy changes are normally quoted at standard conditions:
100kPa Pressure
298K (room temp, 25 degrees C)
Solutions at 1 moldm^-3
All substances should have their normal state at 298K
What is the standard enthalpy change of the formation of a compund?
The enthalpy change when 1 mole of the compound is formed from its elements under standard conditions (298K and 100kPa), all reactants and products being in their standard states
What is the standard enthalpy change of combustion?
The enthalpy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions (298K and 100kPa), all reactants and products being in their standard states
