C7(Energy Changes) Flashcards
What is the law of conservation of energy
Energy is conserved in chemical reactions, It’s neither created or destroyed
An exothermic reaction is …
A reaction in which energy is transferred from the substance to the surroundings
An endothermic reaction is …
A reaction in which energy is transferred to the substance from their surroundings
Exothermic changes can be used in ….
-Hand warmers
-Self heating cans
Endothermic changes can be used in …
-Cold packs
-Sports injuries
Bond breaking is
Endothermic
Bond making is …
Exothermic
In bonding In an exothermic reaction ….
The energy released when new bonds are formed is greater than the energy absorbed when bonds are broken
In bonding In an endothermic reaction
The energy released when new bonds are formed is less than the energy absorbed when bonds are broken
Bond energy is …
The energy needed to break the bond between two atoms
Chemical cells and batteries work when …
-2 metals are dipped in a salt solution and joined by a wire, the more reactive metal will donate electrons to the less reactive metal
-The greater the difference in reactivity between the two metals, the higher the voltage produced by the cell
How do hydrogen fuel cells work
-Oxygen gas is supplied to the anode and reacts to form hydroxide ions
-Hydrogen gas is supplied as a fuel to the cathode and it oxidises with hydroxide ions to form water and provides a source of electrons
Advantages of hydrogen fuel cells ….
-Do not need to be electrically recharged
-No pollutants are produced
-Can be a range of sizes for different uses
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
