Energy changes

• What is an exothermic reaction?

  A reaction where energy is transferred to the surroundings. Temp of sureoundings increase
• What is an example of an exothermic reaction?

  Combustion reactions, neutralisation reactions, oxidation reactions
• What is an everyday example of an exothermic reaction?

  hand warmers

  Self heating cans
• What is an endothermic reaction?

  a reaction that takes in energy from its surroundings. Temp of surroundings decreases.
• What is an example of an endothermic reaction?

  Thermal decomposition reactions

  The reaction of citric acid and sodium hydrogencarbonate.
• What is an everyday life example of an endothermic reaction?

  Instant ice packs
• RP- how do you investigate the variables that affect temperature changes in reacting solutions?

  Place polystyrene cup inside the glass beaker to make it more stable

  Measure an appropriate volume of each liquid.

  Place one of the liquids in a polystyrene cup

  Record temp of solution

  Add the second solution and record the highest or lowest temperature obtained.

  Change the independent of one of the reactants (conc, acid, metal)
• What does an exothermic reaction profile look like?

  products have less energy than reactants
• What does an endothermic reaction look like?

  Products have more energy than reactants
• What is activation energy?

  the minimum amount of energy needed to start a chemical reaction
• How can you tell a reaction is exothermic from a reaction profile?

  The overall change is negative. Products have less energy than reactants.
• What reaction type breaks bonds?

  endothermic
• How can you tell that a reaction is endothermic from a reaction profile?

  Overall change is positive. Products have more energy than reactants
• What reaction type forms bonds?

  Exothermic
• What is bond energy?

  The energy required to break one mole of a covalent bond
• How do you calculate energy change?

  energy in - energy out
• What is a chemical cell?

  A store of internal energy that can be transferred as an electric current in a circuit.
• What does the voltage of a cell depend on?

  The type of electrode and electrolyte
• What is a simple cell made of?

  Two different metals in contact with an electrolyte
• Why can rechargeable cells and batteries be recharged?

  because the chemical reactions are reversed when an external electrical current is supplied
• Why do non-rechargeable batteries stop working?

  The reactants get used up and the chemical reactions stop.
• What affects the voltage of a cell?

  The reactivity between the two pieces of metal in the cells.
• What are fuel cells?

  Device that produces a voltage continuously when supplied with a fuel and oxygen.
• What is the only product of a hydrogen oxygen fuel cell?

  water
• What is an advantage of alkaline cells?

  Cheap to manufacture
• What is a disadvantage to alkaline cells?

  May end up in landfill sites once fully discharges: expensive to recycle.
• What is an advantage to rechargeable cells?

  Can be recharged many times before being recycled. Resulting use of recourses.
• What is a disadvantage to rechargeable cells?

  Costs more to manufacture
• What is an advantage to hydrogen fuel cells?

  Easy to maintain as there are no moving parts. Water is the only chemical product.
• What is a disadvantage to hydrogen fuel cells?

  Very expensive to manufacture, needs a constant supply of hydrogen fuel which is flammable.
• What are hydrogen oxygen fuel cells used in?

  Spacecrafts.
• • How can you tell a reaction is exothermic from a reaction profile?

  The overall change is negative. Products have less energy than reactants.