energy changes in reactions Flashcards
(15 cards)
What is conserved in chemical reactions?
Energy
This principle is known as the law of conservation of energy.
Define an exothermic reaction
A reaction that transfers energy to the surroundings, increasing their temperature.
Give examples of exothermic reactions.
- Combustion
- Many oxidation reactions
- Neutralisation
What are everyday uses of exothermic reactions?
- Self-heating cans
- Hand warmers
Define an endothermic reaction
A reaction that takes energy in from the surroundings, decreasing their temperature.
Give examples of endothermic reactions.
- Thermal decompositions
- Reaction of citric acid and sodium hydrogencarbonate
What is an everyday use of an endothermic reaction?
A sports injury pack
What is activation energy?
The energy needed for a reaction to occur.
On a reaction profile, how is activation energy represented?
As the distance from the energy of the reactants to the top of the curved line showing the energy.
What does it indicate if reactants have more energy than products on a reaction profile?
Energy has been released and the reaction is exothermic.
What does it indicate if products have more energy than reactants on a reaction profile?
Energy has been taken in and the reaction is endothermic.
What is needed to break bonds?
Energy
What happens when bonds are made?
Energy is released.
In an exothermic reaction, what is greater: energy released from forming new bonds or energy needed to break existing bonds?
Energy released from forming new bonds.
In an endothermic reaction, what is greater: energy needed to break existing bonds or energy released from forming new bonds?
Energy needed to break existing bonds.
