P2C19 - Heat energy changes in chemical reactions Flashcards
Why do energy changes take place?
Because of a chemical reaction
In what examples does a heat energy change happen?
Precipitate reactions
Neutralisation reactions
Displacement reactions
Salt dissolved in water
What is a neutralisation reaction?
The reaction between an acid and a base
What is a displacement reaction?
When a more reactive metal takes the place of a less reactive metal.
Why is salt dissolving in water an example of a chemical reaction where an energy change takes place?
Ionic bonds in a salt break.
What is a precipitate reaction?
When two solutions react to make an insoluble salt.
What is an exothermic reaction?
Energy is transferred to the surroundings
What are some examples of an exothermic reaction?
Oxidation
Combustion
Handwarmers
Neutralisation
What is an endothermic reaction?
Energy from the surroundings is transferred to the reacting chemicals.
What are some examples of an exothermic reaction?
Thermal decomposition
Citric acid + baking soda
Cooling packs
Do exothermic reactions bond make or bond break?
Bond make.
Do endothermic reactions bond make or bond break?
Bond break.
What is the equation for energy change in a reaction?
Energy change = Total bond energies of reactants − Total bond energies of products
What unit is normally used for measuring bond energies?
kJ / mol
How do you know if a reaction is endothermic?
If the total energy released by forming bonds is LESS than total energy required to break bonds.
