C11 Energy Changes Flashcards
What is an exothermic energy transfer?
transfer to surrounding
(gets hotter)
Example of exothermic energy transfers
Oxidation
Combustion
Neutralisation
What is an endothermic energy transfer?
Transfer from the surroundings to the object
(gets colder)
Example of endothermic energy transfers
Thermal decomposition
Sports injury packs
What is a reaction profile?
Diagram showing how 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 can be used to lower the activation energy?
Catalysts
What is bond energy?
Energy required to break a bond
OR
The energy released when a bond is formed
In terms of bonds what is an exothermic reaction?
LESS energy is required to break the bonds than is released when making the bonds
In terms of bonds 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 (electrolytes)
What is a battery?
Two or more chemical cells connected in series
How does the p.d of a cell depend on metals that the electrodes are made of?
Bigger the difference in reactivity, the greater the p.d
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 a hydrogen fuel cell, what is the overall reaction?
2H2 + O2 —> 2H2O
Advantage of a hydrogen fuel cell
only product is water
does not need to be electrically recharged
Disadvantages of hydrogen fuel cells
-Hydrogen is flammable
-Difficult to store
-Produced from non-
renewable sources
