5 - energy changes Flashcards
What happens when two different metals are placed into an electrolyte with a wire connected to them? (CB EC Ch)
we can produce electricity
What is an electrolyte and an example? (CB EC Ch)
a solution that can conduct electricity, for example a solution of an ionic compound.
What is the setup of a cell? (CB EC Ch)
an electrolyte with two metals (that are very different on the reactivity scale) and a voltmeter connecting the two.
a reading will apear on the voltmeter as there is a potential difference as there is an electric current.
What are the key points of cells and batteries? (CB EC Ch)
- a cells can only produce electricity for a certain period of time. Eventually, the chemicals in the cell run out and the reaction stops.
- cells only produce elecricity if we use metals with different reactivities
- the greater the difference between the reactivity, the greater the potential difference.
- the electrolyte also affects the potential difference
What does the size of the potential difference in a cell depend on? (CB EC Ch)
the difference in the reactivity series.
What is a battery? (CB EC Ch)
two or more cells connected together in series to produce a greater voltage
What is an example of a non-reachargable battery? (CB EC Ch)
an alkaline battery
How can rechargable battery be reacharged? (CB EC Ch)
reversing the chemical reaction when we apply an electrical current.
What are the reactants in a fuel cell? (FC EC CH)
Hydrogen and pure oxygen or air
What is the waste product of the reactions in fuel cells? (FC EC Ch)
water
What is the half equation for the reaction at the cathode in fuel cells? (FC EC Ch)
2H2 ______> 4H+ + 4e-
2 lots of two hydrogens bonded together is made by 4 positive hydrogen ions and 4 negative electrons
Where does the electrical current come from in fuel cells? (FC EC Ch)
From the reaction happening at the cathode. The hydrogen atom splits into hyrdogen ions and electrons which then form the electrical current.
What is the half equation for the anode in fuel cells? (FC EC Ch)
O2 + 4H+ + 4e- ________> 2H2O
oxygen and hydrogen ions and electrons form 2 water
What is the overall equation for the hydrogen fuel cell? (FC EC Ch)
2H2 + O2 _______> 2H2O
the hydrogen is being oxidised
What are the main advantages of using hydrogen fuel cells compared to rechargable batteries? (FC EC Ch)
- they can produce electricity for as long as you provide hydrogen .
rechargable batteries run out and need to be recharged - hydrogen fuel cells do not get less efficient the longer they run
rechargable batteries can store less electricity the more charging cycles they go through and eventually need to be replaced - Hydrogen fuel cells can be a source of drinking water e.g space-craft
What are some problems with hydrogen fuel cells compared to rechargeable batteries? (FC EC Ch)
- run on hydrogen which is an explosive gas and is very difficult to store safely
no dangerous fuels are required. but some can catch fire if not manufactured correctly - produce a relativley low potential difference or voltage so several are needed together.
can produce a greater potential difference than hydrogen fuel cells.
Where is the energy change on an energy profile diagram? (EER EC Ch)
the space between the reactants and the products.
what is the activiation energy? (EER EC Ch)
the minimum amount of energy that particles must have in order to react.
