C7: Energy Changes Flashcards
what is an exothermic reaction
transfer to the surroundings
what is an endothermic reaction
transfer from the surroundings
what is a reaction profile
diagram showing the energy changes in a reaction
what is the activation energy
minimum amount of energy required before a collision will result in a reaction
what is bond energy
the energy required to break a bond or the energy released when a bond is formed
In terms of bond breaking and making, what is an exothermic reaction
less energy is required to break the bonds than is released when making the bonds
in terms of bond breaking and making what is an endothermic reaction
more energy is required to break the bonds than is released when making the bonds
how are chemical cells made
connect two different metals (electrodes) in a solution (electrolyte)
what is a battery
two or more chemical cells connected in series
how does the potential difference of a cell depend on the metals that the electrodes are made of
the bigger the difference in reactivity, the greater the potential difference
how can some cells be recharged
by applying an external current
why can some cells not be recharged
the reaction cannot be reversed
what is a fuel cell
cell that uses a fuel and oxygen to generate electricity
in the hydrogen fuel cell, what is the overall reaction
2H2(g)+O2(g)→2H2O(l)
in the alkaline hydrogen fuel cells, what are the half equations
2H2(g) + 4OH−(aq) ➞ 4H2O(l) + 4e−
O2(g) + 2H2O(l) + 4e− ➞ 4OH−(aq)
