C5 - Energy Changes Flashcards
What is an exothermic reaction?
A reaction where energy is transferred to the surroundings. So the surrounding temperature increases.
Give examples of exothermic reactions.
Combustion, respiration and many neutralisation reactions
What is an endothermic reaction?
A reaction where energy is transferred from the surroundings. So the surrounding temperature decreases.
Give examples of endothermic reactions.
Thermal decomposition reactions, the reaction between citric acid and sodium hydrogencarbonate, photosynthesis
What is the activation energy?
The minimum energy needed to break bonds to start a reaction.
If the reactants have more energy than the products, what kind of a reaction must have taken place?
An exothermic one. Energy has been transferred to the surroundings.
If the reactants have less energy than the products, what kind of a reaction must have taken place?
An endothermic one. Energy has been taken in from the surroundings.
Is breaking bonds endothermic or exothermic?
Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other)
Is making bonds endothermic or exothermic?
Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy)
How do we work out the energy change from a reaction profile?
The difference between the energy of the reactants and the energy of the products
What is the collision theory?
Collisions between reacting particles are needed for chemical reactions to take place. These collisions must have sufficient energy (the activation energy).
What is the conservation of energy principle?
Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as it was before the reaction.
What is a reaction profile?
A graph which shows the relative energies of the reactants and products, as well as the activation energy of the reaction.
What occurs in a chemical reaction in terms of bond energies?
Energy is absorbed to break bonds. Energy is released when bonds are formed.
Describe exothermic and endothermic reaction in terms of bonds breaking/forming.
Endothermic - energy that is absorbed to break bonds is greater than what is released to make bonds
Exothermic - energy that is released to make bonds is greater than what is absorbed to break bonds
