Energy Changes C7 Flashcards
Write a method for calculating temperature changes in a neutralisation reaction
- Measure 30 cm^3 of HCl into a polystyrene cup (insulator)
- Put a thermometer through the hole in the lid and measure the starting temperature
- Add 5 cm^3 of NaOH into the cup
- Measure the maximum temperature reached (when it stops increasing)
- Repeat until 40 cm^3 of NaOH has been added
What is an exothermic reaction?
A reaction that transfers energy from the system to the surroundings (emits energy)
What is an endothermic reaction?
A reaction that transfers energy from the surroundings to the system (takes in energy)
What is the system?
The reactants and products
What is the surroundings?
Anything not in the reactants (e.g. flask, beaker, air)
What is the universe?
The system and the surroundings
What is the activation energy?
The minimum amount of energy required for particles to react
What is an exothermic reaction in terms of making/breaking bonds?
The energy required to break existing bonds is less than the energy released from forming new bonds
What is an endothermic reaction in terms of making/breaking bonds?
The energy required to break existing bonds is greater than the energy released from forming new bonds
How is a simple cell made?
By connecting two different metals in contact with an electrolyte (a salt or acid)
Why are some batteries rechargable?
The reactions are reversed
How does the reactivity of metals in chemical cells affect the voltage?
The greater the difference in reactivity of the two metals, the greater the voltage
How do fuel cells work?
- Fed with oxygen and hydrogen
- They react to produce water
- Energy released is converted into electrical energy
What are some advantages of fuel cells?
- Releases no pollutants
- Don’t need to be recharged
What are some disadvantages of fuel cells?
- Require hydrogen to be produced, often non-renewably
- Hydrogen is flammable
- Hydrogen is difficult to store
