5. Energy Changes Flashcards
(26 cards)
What occurs at the cathode during electrolysis?
Positively charged ions gain electrons, resulting in reduction.
What occurs at the anode during electrolysis?
Negatively charged ions lose electrons, resulting in oxidation.
Provide an example of a half equation at the cathode.
2H+ + 2e- → H2.
Provide an example of a half equation at the anode.
4OH- → O2 + 2H2O + 4e-.
What is an exothermic reaction?
A reaction that transfers energy to the surroundings, increasing their temperature.
Give two examples of exothermic reactions.
Combustion and neutralisation.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings, decreasing their temperature.
Give an example of an endothermic reaction.
The reaction of citric acid and sodium hydrogencarbonate.
What is the activation energy in a chemical reaction?
The minimum amount of energy that particles must have to react.
What do reaction profiles illustrate?
The relative energies of reactants and products, activation energy, and overall energy change.
How can you identify an exothermic reaction from a reaction profile?
By observing that the energy of the products is lower than that of the reactants.
What is the overall energy change in an exothermic reaction?
Energy released from forming new bonds is greater than the energy needed to break existing bonds.
What is the overall energy change in an endothermic reaction?
Energy needed to break existing bonds is greater than the energy released from forming new bonds.
What is the relationship between energy conservation and chemical reactions?
The total energy in the universe remains constant before and after a chemical reaction.
What factors affect the voltage produced by a cell?
The type of electrode and electrolyte used.
What is a simple cell?
A cell made by connecting two different metals in contact with an electrolyte.
What is the difference between non-rechargeable and rechargeable batteries?
Non-rechargeable batteries stop working when reactants are used up, while rechargeable batteries can reverse reactions when supplied with external current.
What is the overall reaction in a hydrogen fuel cell?
The oxidation of hydrogen to produce water.
What are the advantages of hydrogen fuel cells compared to rechargeable batteries?
They offer a potential alternative with different energy production methods.
What is the significance of bond energies in chemical reactions?
They are used to calculate the energy needed to break bonds and the energy released when bonds are formed.
What is the purpose of Required Practical 4 in this chemistry curriculum?
To investigate the variables that affect temperature changes in reacting solutions.
What are the everyday applications of exothermic reactions?
Self-heating cans and hand warmers.
What is the effect of temperature change in endothermic reactions?
The temperature of the surroundings decreases.
What is the role of chemical reactions in cells and batteries?
They produce electricity through chemical reactions.
