ENERGY CHANGES Flashcards
What is an exothermic reaction?
Energy transfer to the surroundings.
What is an endothermic reaction?
Energy transfer from the surroundings to an object.
What happens to the temperature in an exothermic reaction?
The temperature increases.
What happens to the temperature in an endothermic reaction?
It decreases.
Compare the products and reactants in an exothermic reaction?
The products have less energy than the reactants in an exothermic reaction.
Compare the reactants and products in an endothermic reaction?
The products have more energy than the reactants in an endothermic reaction.
What does an acid and an alkali give you?
Salt and water.
What does nitric acid and potassium hydroxide give you?
Potassium nitrate and water.
What does lithium hydroxide and sulphuric acid acid give you?
Lithium sulphate and water.
What ions does an acid release?
Hydrogen ions (H+).
What ions do Alkalis release?
Hydroxide ions (OH-).
Uses of neutralisation?
Indigestion remedied.
Neutralise acidic soil - use calcium hydroxide.
What solid is used in self heating cans?
Calcium
Calcium oxide + water ——> calcium hydroxide.
What is activation energy?
The minimum amount of energy needed before colliding particles of reactants have sufficient energy to cause a reaction. What
What is the energy change in an exothermic reaction?
Chemical -> heat
What is the energy change in an endothermic reaction?
Heat -> chemical
Give examples of where exothermic reactions can be used usefully?
Hand and body warmers.
Self-heating cans
Give examples of where endothermic reactions can be used usefully?
Chemical cold packs.
Chilling cans of drink.
What process in bond breaking?
Endothermic - energy has to be supplied to break chemical bonds therefore energy is taken from the surroundings.
What process in bond making?
Exothermic.
If more energy is released when breaking the bonds in the reactants than when making the new bonds formed in the products what type of reaction is it?
Endothermic.
If more energy is released when making the new bonds than when breaking the bonds in the reactants what type of reaction is it?
Exothermic.
What does the voltage tell you about the reactivity of a metal?
The greater the difference in reactivity between the two metals used, the higher the voltage produced.
How is a simple electrical cell created?
When two metals are dipped in a salt solution and joined by a wire, the more reactive metal will donate electrons to the less reactive metal.
Advantages of hydrogen fuel cells?
Do not need to be electrically recharges.
No pollutants are produced
Can be a range of sizes for different users.
Disadvantages of hydrogen fuel cells?
Hydrogen is highly flammable
Hydrogen is sometimes produced for the cell by non-renewable sources.
Hydrogen is difficult to store.
Talk about how hydrogen fuel cells work.
The cells are fed with hydrogen and oxygen and produce water. Hydrogen gas is supplied as a fuel to the negative electrode. It diffuser through the graphite electrode and reacted with hydroxide ions to form water and provided a source of electrons to an external circuit.
Oxygen gas is supplied to the positive electrode. It diffuser through the graphite and reacts to form hydroxide ions, accepting electrons from the external circuit.
