C7 Flashcards
what is an exothermic reaction
a reaction where the reacting substances give out heat to the surroundings
what is an endothermic reaction
a reaction where the reacting substances take in heat, making the surroundings cooler
what is the difference between bond making and bond breaking?
bond making is exothermic as energy is transferred to the surroundings but bond breaking is endothermic because to break a bond energy is required so it is taken in from the surroundings
what is activation energy
minimum amount of energy needed before colliding particles of reactants have sufficient energy to cause a reaction
how can a bond energy tell you if a reaction is exothermic
if the energy released when bonds are formed is more than the energy needed to break the bonds
how can a bond energy tell you if a reaction is endothermic
if the energy needed to break the bonds is more than the energy released when the bonds are broken
what is bond energy
the energy needed to break the bond between 2 atoms
how do you work out the energy change for a chemical reaction
work out how much energy is needed to break the chemical bonds in the reactants and how much energy is released when new bonds are formed in the products
in electrical cells using metals how can you increase the voltage
use metals with a greater difference in reactivity
how is an electrical cell formed
2 metals are dipped in a salt solution and joined by a wire, the more reactive metal will dontate electrons to the less reactive metal forming an electrical cell
what is a fuel cell
an efficient way of oxidising hydrogen. The cells are fed with hydrogen and oxygen to produce water and the energy released can be used to power a vehicle
how do hydrogen and oxygen act in a fuel cell
hydrogen diffuses through the negative graphite electrode and reacts with hydroxide ions to form water and provide a source of electrons to an external circuiy
oxygen diffuses through the positive graphite electrode and reacts to form hydroxide ions accepting electrons from the external circuit
what are 3 advantages of hydrogen fuel cells
don’t need to be electrically recharged
no pollutants produced
can be a range of sizes fo different uses
what are 3 disadvantages of hydrogen fuel cells
hydrogen is highly flammable
somtimes hydrogen is produced by non reneweable sources
hydrogen is difficult to store
