C5 Flashcards
What’s an exothermic reaction?
An exothermic reaction is one that transfers energy to the surroundings so the temperature of the surroundings increases
What are examples of exothermic reactions (3)?
Exothermic reactions include combustion, many oxidation reactions and neutralisation.
What are everyday examples of exothermic reactions?
Self-heating cans and hand warmers.
What is an endothermic reaction?
An endothermic reaction is one that takes in energy from the surroundings so the temperature of the surroundings decreases
What are some examples of endothermic reactions?
Endothermic reactions include thermal decompositions and the reaction of citric acid and sodium hydrogencarbonate.
What are some everyday examples of endothermic reactions?
Some sports injury packs are based on endothermic reactions
Practical 4 - investigate the variables that affect temperature changes in reacting solutions
- Place the polystyrene cup inside the glass beaker to make it more stable. 2. Measure an appropriate volume of each liquid, eg 25 cm3. 3. Place one of the liquids in a polystyrene cup. 4. Record the temperature of the solution. 5. Add the second solution and record the highest or lowest temperature obtained. 6. Change your independent variable and repeat the experiment.
What is the activation energy?
The minimum amount of energy needed to start a chemical reaction.
Reaction profile for exothermic
Starts high energy, up with activation energy then down.
Reaction profile for endothermic
Low energy at the beginning, up with activation energy, then levels out (still higher)
What 2 things happen during a reaction?
- energy must be supplied to break bonds in the reactants 2.energy is released when bonds in the products are formed.
What about the energy from an exothermic reaction?
In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
What about the energy from an endothermic reaction?
In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
What do cells contain?
Cells contain chemicals which react to produce electricity.
The voltage produced by a cell is dependent upon a number of factors including…
the type of electrode and electrolyte
How can a simple cell be made?
A simple cell can be made by connecting two different metals in contact with an electrolyte.
What is a battery?
Batteries consist of two or more cells connected together in series to provide a greater voltage
Summary about non - rechargeable cells and example
In non-rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up. Alkaline batteries are non-rechargeable
Summary about rechargeable cells and example
Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied
What is a fuel cell?
An electrical cell that is supplied with a fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently.
How does a fuel cell work?
- Hydrogen enters anode and oxygen goes to cathode compartment. 2. Hydrogen loses electrons to form H+ ions which is oxidation. 3. It moves to the cathode. 4. Oxygen is reduced and gains electrons to make water.
With fuel cells what’s the half equation at the cathode?
H2 –> 2H+ + 2e-
With fuel cells what’s the half equation at the anode?
O2 + 4H+ + 4e- –) 2H2O
What are advantages of hydrogen fuel cells?
They produce water, which is not a pollutant.
What are disadvantages of hydrogen fuel cells?
H2 is a gas which takes up more space. H2 is explosive with air. Either made from hydrocarbons or electrolysis which still uses electricity.
