Unit 3 - Energy from Reactions Flashcards
How can you measure the amount of energy released by a chemical reaction? (in solution)
Taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction
What is an exothermic reaction?
A reaction which gives out energy to the surrounding, usually in the form of heat and usually shown by a rise in temperature
What is an endothermic reaction?
One which takes in energy from the surrounding, usually in the form of heat and usually shown by a fall in temperature
What happens during a chemical reaction?
Old bonds are broken and new bonds are formed
What process is breaking bonds?
Endothermic
What process is bond forming?
Exothermic
In an endothermic reaction, what is they energy required to break old bonds?
Greater than the energy released when new bonds are formed
In an exothermic reaction what is the energy required for bond formation?
Greater than the energy used in breaking old bonds
How is fuel energy calculated?
Using calorimetry
How do you measure the amount of energy release when a fuel is burnt?
Burn the fuel and use the flame to heat up some water - this is calorimetry
What is the method for calorimetry?
- Put 50cm of water in the copper can and record its temperature
- Weigh the spirit burner and lid
- Put the spirit burner underneath the can, and light the wick. Heat the water, stirring constantly, until the temperature reaches bout 50℃
- Put out the flame using the burner lid, and measure the final temperature of the water
- Weigh the spirit burner and lid again
In energy level diagrams: what does an exothermic reaction look like?
The products are at a lower energy than the reactants
aka
Reactants
Products
In energy level diagrams: What does the difference in heigh represent in an exothermic reaction?
The energy given out in the reaction (per mole)
In energy level diagrams: what does the intial rise represent?
The energy needed to break the old bonds (the activation energy)
In energy level diagrams: what do endothermic reactions look like?
The products are at a higher energy than the reactions
aka
Products
Reactants
In energy level diagrams: what does the difference in height represent in endothermic reactions?
The energy taken in during the reaction (per mole)
What is the activation energy?
The minimum energy needed by reacting particles to break their bonds
What do catalysts do to activation energy?
lowers it
how is the change in activation energy made by a catalyst represented on a energy level diagram?
By the same curve but lower down
What do hydrogen and oxygen react together to produce?
Water
is the reaction between hydrogen and oxygen endothermic or exothermic?
exothermic (releases energy)
Hydrogen gas can be burn in oxygen as a fuel in the..
combustion engines of vehincles
Pro’s of reacting hydrogen in oxygen in a combustion engine?
Hydrogen combines with oxygen in the air to form just water so its very clean
Cons of reacting hydrogen in oxygen in a combustion engine?
You need a special, expensive engine
Hydrogen is very hard to store safely as its very explosive
What is a fuel cell?
An electrical cell that’s supplied with a fuel and oxygen and uses energy to form the reaction between them to generate electricity
What cell can hydrogen be used in?
A hydrogen-oxygen fuel cell
Advantages of fuel cells?
More practical than solar cells
Safer than nuclear power
Don’t produce any conventional pollutants
They would eventually help countries to become less indepentant on crude oil
