Energy Changes Flashcards
What is an exothermic reaction?
Energy is transferred to the surroundings (exits)
What happens to the temperature of an exothermic reaction?
Temperature increases
What is an endothermic reaction?
Energy is taken in from the surroundings
What happens to the temperature of an endothermic reaction?
Temperature decreases
Give examples of exothermic reactions.
Combustion, Neutralisation, Respiration, Oxidation reactions, Self-heating cans, Hand warmers
Give everyday uses of exothermic reactions.
Self-heating cans, Hand warmers
Give examples of endothermic reactions.
Thermal decomposition, Photosynthesis, Citric acid and sodium hydrogen carbonate (sherbet)
Give everyday uses of endothermic reactions.
Sports injury packs
What is the energy of the products compared to reactants in an exothermic reaction?
Less
What is the energy of the products compared to reactants in an endothermic reaction?
More
What is activation energy?
Minimum energy that particles must have for a reaction to occur
What does a reaction profile show?
It is a graphical representation of energy vs reaction (represented as a hump going from the reactants)
What is needed to break a bond?
Energy is required to break a bond.
What type of process is bond breaking?
Endothermic process.
What is given out when a bond is made?
Energy is released when a bond is made.
What type of process is bond making?
Exothermic process.
Why is a reaction endothermic overall in terms of bonds breaking and making?
More energy is taken in during bond breaking than is given out during bond making.
Why is a reaction exothermic overall in terms of bonds breaking and making?
More energy is given out during bond making than is taken in during bond breaking.
How can you calculate the overall energy change in a reaction?
Sum of bonds broken - sum of bonds made (reactants - products).
What do cells contain?
Cells contain chemicals which react to produce electricity.
What is the voltage of a cell dependent on?
Type of electrode (different metals), concentration of electrolyte, and temperature.
How can a simple cell be made?
By connecting two different metals with an electrolyte.
What is an electrolyte?
A liquid that contains ions which react with the electrode.
How does the voltage produced in a cell represent the reactivity of the metals?
The larger the difference in reactivity between the two metals, the larger the voltage.
What is a battery?
Two or more cells connected together in series to provide a greater voltage.
What are non-rechargeable cells and batteries?
The chemical reaction is irreversible and stops when one of the reactants has been used up.
What is an example of a non-rechargeable battery?
Alkaline batteries are non-rechargeable.
What are rechargeable cells and batteries?
Rechargeable cells and batteries can be recharged and used multiple times.
What is a fuel cell?
A fuel cell is a device that converts chemical energy from a fuel into electricity through chemical reactions.
How are fuel cells and chemical cells different?
Fuel cells oxidise the fuel electrochemically, while in chemical cells, the fuel is burned.
What is a common fuel used in a fuel cell?
Hydrogen is a common fuel used in a fuel cell.
What solutions can be used as the electrolyte in a hydrogen fuel cell?
An alkali (e.g., potassium hydroxide) or an acid (e.g., hydrochloric acid) can be used as the electrolyte.
What happens at the negative electrode (anode) in a hydrogen fuel cell?
Hydrogen is oxidised, losing electrons.
H2 → 2H* + 2e
What happens at the positive electrode (cathode) if the electrolyte is an alkali?
Oxygen reacts with water to produce hydroxide ions, using up electrons.
What happens at the positive electrode (cathode) if the electrolyte is an acid?
Oxygen is reduced, gaining electrons to form water.
O2 + 4H* + 4e* → 2H2O
What happens at the negative electrode (anode) if the electrolyte is an acid?
Hydrogen is oxidised, losing electrons.
H2 → 2H* + 2e
What is the overall equation for the hydrogen fuel cell?
2H2 + O2 → 2H2O
Hydrogen + oxygen → water
What are the requirements for fuel cells to produce voltage continuously?
A supply of a suitable fuel and oxygen are required.
What are the advantages of a hydrogen fuel cell?
Advantages include no pollutants produced, only water and heat as byproducts, faster refueling, longer travel distances, and potential for renewability.
What are the disadvantages of a hydrogen fuel cell?
Disadvantages include hydrogen being explosive, higher costs to refuel and manufacture, and limited hydrogen filling stations.
