exo and endo

• What is conserved in chemical reactions?

  Energy is conserved in chemical reactions.
• What happens to energy during a chemical reaction?

  Energy is transferred to or from the surroundings.
• What is an exothermic reaction?

  An exothermic reaction transfers energy to the surroundings.
• What is the effect of an exothermic reaction on the temperature of the surroundings?

  The temperature of the surroundings increases.
• What are examples of exothermic reactions?

  • Combustion reactions
  • Many oxidation reactions
  • Most neutralisation reactions
• What are everyday uses of exothermic reactions?

  Self-heating cans and hand warmers.
• What is an endothermic reaction?

  An endothermic reaction takes in energy from the surroundings.
• What is the effect of an endothermic reaction on the temperature of the surroundings?

  The temperature of the surroundings decreases.
• What are examples of endothermic reactions?

  • Thermal decomposition reactions
  • Reaction of citric acid and sodium hydrogencarbonate
• What are everyday uses of endothermic reactions?

  Instant ice packs for treating sports injuries.
• What does the slideshow describe regarding exothermic and endothermic reactions?

  It describes an exothermic reaction between sodium hydroxide and hydrochloric acid and an endothermic reaction between sodium carbonate and ethanoic acid.
• What is produced in the exothermic reaction between sodium hydroxide and hydrochloric acid?

  Sodium chloride and water.
• What happens to the thermometer during the exothermic reaction between sodium hydroxide and hydrochloric acid?

  The thermometer shows a rise in temperature.
• What is produced in the endothermic reaction between sodium carbonate and ethanoic acid?

  Sodium ethanoate, water, and carbon dioxide.
• What happens to the thermometer during the endothermic reaction between sodium carbonate and ethanoic acid?

  The thermometer shows a fall in temperature.
• What is the aim of the required practical on temperature changes in reacting solutions?

  • To investigate the variables that affect temperature changes in reacting solutions.
• What apparatus is used in the required practical?

  • Polystyrene cup
  • Thermometer
  • 250 cm³ glass beaker
  • Measuring cylinder
  • Top pan balance
• What are some chemical reactions you could investigate in the practical?

  • Acids reacting with metals
  • Acids reacting with metal carbonates
  • Acids reacting with alkalis
  • Displacement reactions of metals
• What is the method for reacting two solutions in the practical?

  1. Place the polystyrene cup inside the glass beaker.
  2. Measure an appropriate volume of each liquid.
  3. Record the temperature of the solution.
  4. Add the second solution and record the temperature change.
  5. Change the independent variable and repeat.
• What is the method for reacting a solid with a solution in the practical?

  1. Place the polystyrene cup inside the glass beaker.
  2. Measure an appropriate volume of the solution.
  3. Measure an appropriate mass of the solid.
  4. Record the temperature of the solution.
  5. Add the solid and record the temperature change.
  6. Change the independent variable and repeat.
• What does a bigger temperature change in a reaction indicate?

  More energy is absorbed or released.
• What is the biggest source of error in the temperature change experiment?

  Unwanted heat transfer.
• What precautions should be taken when using dilute acids and alkalis?

  • Avoid contact with skin
  • Rinse off skin if necessary
  • Wear eye protection
• What precautions should be taken when using solutions of metal salts?

  • Dispose of metal salt solutions as advised by the teacher
  • Some metal salts are collected for safe disposal
• What does an energy level diagram show?

  It shows whether a reaction is exothermic or endothermic.
• What happens to energy in an exothermic reaction according to the energy level diagram?

  The energy level decreases because energy is given out to the surroundings.
• What happens to energy in an endothermic reaction according to the energy level diagram?

  The energy level increases because energy is taken in from the surroundings.
• What is a reaction profile?

  • A diagram that shows how the energy of the chemicals changes during the reaction.
  • Includes activation energy, which is the minimum energy needed for a reaction to occur.
• What is activation energy?

  It is the minimum energy needed by particles when they collide for a reaction to occur.
• How is the overall change in energy in a reaction calculated?

  It is the difference between the energy of the reactants and products.
• What happens during a chemical reaction regarding bonds?

  • Bonds in the reactants are broken.
  • New bonds are made in the products.
• What determines whether a reaction is exothermic or endothermic?

  The difference between the energy needed to break bonds and the energy released when new bonds are made.
• What is bond energy?

  It is the amount of energy needed to break one mole of a particular covalent bond.
• How do you calculate the energy change for a reaction using bond energies?

  1. Add together the bond energies for all the bonds in the reactants (energy in).
  2. Add together the bond energies for all the bonds in the products (energy out).
  3. Energy change = energy in - energy out.
• What is the energy change for the reaction of hydrogen and chlorine to form hydrogen chloride gas?

  • 185 kJ mol^-1
• What is the energy change for the decomposition of hydrogen bromide?

  +103 kJ mol^-1