Seneca C5 Flashcards
What are Exothermic Reactions
Energy from the reacting chemicals is transferred to the surroundings, which often increase in temperature as a result
What are examples of Exothermic Reactions
Combustion.
Neutralization.
Oxidation.
What are Endothermic Reactions
Energy from the surroundings is transferred to the reacting chemicals, causing the temperature of the surroundings to decrease
What are examples of Endothermic Reactions
Thermal decomposition.
The reaction that happens when citric acid is combined with sodium hydrogen carbonate (sodium bicarbonate).
What are the 2 main requirements for a successful reaction to take place
. Collisions
. Activation Energy
What is activation energy
The activation energy is the minimum amount of energy that reacting particles must have for a reaction to happen.
What do reaction profiles tell us
. The amount of energy contained within the reactants and the products.
. The activation energy of a reaction.
. The overall energy change that happens as a result of a reaction.
How can catalysts increase reaction rates
. By lowering the activation energy
What is bond energy
All chemical bonds have a “bond energy” that measures the strength of chemical bonds
How can we see if a reaction is exothermic or endothermic (bond energy)
By subtracting the total bond energies of the products from the total bond energies of reactants, we can see if a reaction is endothermic or exothermic
Exothermic reactions (bond energy)
Energy released by making bonds > energy required to break bonds
Endothermic reactions (bond energy)
Energy released by making bonds < energy required to break bonds
Bond breaking
Bond breaking requires energy and thus is an endothermic process
Bond making
Bond making releases energy and thus is an exothermic process
Bond energy
This is a measure of the strength of chemical bonds. The units are kilojoules per mole (kJ/mol)
How do we make a simple cell
We can make a simple cell by connecting 2 different electrodes and putting them in a liquid electrolyte
The difference in the reactivity of the metals produces a voltage
How do we change the voltage output of a cell
. Changing the type of electrode
. Changing the type of electrolyte
. Changing both
Changing the type of electrode
A greater difference in reactivity between the two electrodes will result in the cell having a greater voltage
Changing the type of electrolyte
Changing the electrolyte changes the reactions that happen at the electrodes. This will result in the voltage output of the cell changing.
In a chemical cell, what effect will increasing the difference in reactivity between the two electrodes have on voltage output?
Increasing voltage output
In a chemical cell, what effect will decreasing the difference in reactivity between the two electrodes have on voltage output?
Decreasing voltage output
What is a battery
A battery is a collection of more than one cell joined in series (end-to-end).
How is the voltage of a battery calculated
The voltage of a battery is calculated as the sum of the voltages of its individual cell components.
What happens when the chemicals inside a battery run out
When the chemicals in a battery run out, the battery can not be used anymore.
A battery that has a voltage output of 9V is made up of 3 identical cells. What is the voltage output of each of its individual cell components?
3V
Rechargeable cells/ batteries
In rechargeable cells and batteries, connection to an electric current reverses the reactions that happen at the electrodes.
This means that electricity can continue to be produced as long as there is access to this external electric current.
Non - rechargeable cells/ batteries
In non-rechargeable cells and batteries (e.g. alkaline batteries), irreversible reactions take place at the electrodes.
This means that electricity can no longer be produced as soon as one of the reacting chemicals has run out.
How are cells connected together in batteries?
In series
What are the advantages of fuel cells
. Reliable
. High efficiency
. Less pollution
. Compact and lightweight
The reaction of fuel cells
The reaction is between an external fuel source and oxygen. Once added to the cell, the fuel is oxidized, and this causes a voltage to be established.
What is the waste product of hydrogen fuel cells
In hydrogen fuel cells, the oxidation of hydrogen generates a voltage and the only waste product is water
What is the overall equation for a hydrogen fuel cell?
2H2 + O2 → 2H2O
What are the risks of hydrogen fuel cells
. Hydrogen has to be stored at a high pressure and hydrogen gas is explosive
Why are hydrogen fuel cells better than rechargeable batteries and cells
. Less toxic
. Higher lifetime
. Higher capacity
Why are fuel cells reliable
They don’t have any moving parts
