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
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 sodium hydrogen carbonate
- 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
What is a cell?
A cell is composed of two electrodes dipped in an electrolyte solution. It produces current from a chemical reaction.
What is a battery?
Two or more cells connected in series.
What determines the voltage obtained from a cell?
Identities of metals used as electrodes.
Concentration and identity of electrolyte.
Temperature of electrolyte.
Explain rechargeable batteries.
Chemical reactions are reversed when external current is supplied.
Explain non-rechargeable batteries.
All reactants are used up, cannot be recharged.
What is a fuel cell?
Fuel cells consist of fuel and oxygen. Where the fuel is oxidised to produce electricity.
What is a hydrogen fuel cell?
Where hydrogen is oxidised to form water.
Why should batteries not be put in household waste?
Alkaline waste can be harmful / toxic / corrosive.
What are the adv. of alkaline cells?
Cheap to manufacture.
What are the disadvantages of alkaline cells?
Expensive to recycle.
Toxic waste.
May end up in landfill sites.
