energy changes Flashcards
What is an exothermic reaction?
A reaction that transfers energy to the surroundings
What are some examples of exothermic reactions?
combustion, neutralisation, some oxidation reactions
What is an endothermic reaction?
a reaction which takes in energy from the surroundings
What are some examples of endothermic reactions?
thermal decomposition, citric acid and sodium hydrogencarbonate reaction
Describe the energy transfer required practical
1.put 25cm^3 of 0.25mol/dm^3 of hydrochloric acid and sodium hydroxide in separate beakers
2. Put both beakers in a water bath until they both reach 25 degrees
3. Add both liquids to a polystyrene cup with a lid and a thermometer, insulated by a beaker filled with cotton wool
4. take the temperature of the mixture every 30 seconds, recording the highest temperature
5. repeat, increasing the concentration of hydrochloric acid
Describe what happens to the bonds in an exothermic reaction
More heat energy is released from forming bonds than is used breaking bonds
Describe what happens to the bonds in an endothermic reaction
More thermal energy is used breaking bonds than is released forming bonds
What is activation energy?
The minimum amount of energy the reactants need to collide with each other and react
What is an electrochemical cell?
A system made up of two different electrodes in contact with an electrolyte that generates a potential difference
How do electrochemical cells work?
The chemical reactions between the electrodes and the electrolyte set up a charge difference which flows through the wire, generating electricity
What does the voltage of an electrochemical cell depend on?
The difference in reactivity of the electrodes
Why do non rechargeable batteries stop working eventually?
The chemical reactions that happen at the electrodes are irreversible and the reactants get used up
What is a fuel cell?
An electrical cell that is supplied with fuel and oxygen and uses energy from the reaction to produce electricity
What are the advantages of fuel cells?
they produce fewer pollutants, only by products are water and heat, cheaper than batteries, store more energy than batteries
