energy changes

• what is an exothermic reaction

  transfer energy from the reacting chemicals to their surroundings. the energy transferred from the chemical reaction often heats up the surroundings eg. burning of fuels
• what is an endothermic reaction

  transfer energy from the surroundings to the reacting chemicals. the energy cause a fall in temperature to happen. eg eating sherbet
• the products of exothermic reactions have a lower energy content than the reactants
• whats the method of the required practical for an endo/exo thermic reaction

  1.use the 50cm measuring cylinder to put in 30cm of dilute hydrochloric acid into the polystyrene cup

  2.stand cup inside beaker

  3.use the thermometer to measure the temp of acid

  4.pour the sodium hydroxide into the cup, fit the lid and gently stir the solution through the hole with thermometer

  5.when reading stops changing record the temperature

  6.repeat steps 4 and 5 to add a further 5cm amount of sodium hydoxide, a total of 40cm should be added
• explain the results of the practical

  as you add more acid the temperature begins to increase until it reaches its maximum temperature of 30.5 degrees and then it begins to decrease. this is an example of an exothermic reaction
• why do we use polystyrene cups?

  1.insulation

  2.stops heat transferring from our hands into the practical

  3.stops us from getting burnt
• Exothermic reactions release energy, while endothermic reactions absorb energy.
• what are physical processes of endothermic reactions:

  melting (e.g., ice into water) evaporation, cooking, splitting gas
• what are physical processes of exothermic reactions

  condensation (eg. cloud formation)

  freezing (eg. water to ice)

  dissolving anhydrous salt and water
• if the energy change is negative, the reaction is exothermic if the energy change is positive it is endothermic
• in a reaction profile, the reactants are always on the left and the products are always on the right
• in a reaction profile, if the reaction is an exothermic reaction, the products would be at a lower energy level than the reactants (drawn lower than the reactants)
• in a reaction profile, if the reaction is an endothermic reaction, the products would have a higher energy level than the reactants (drawn higher than the reactants)
• bond breaking is an endothermic reaction, bond making is a exothermic reaction
• what is activational energy

  the minimum amount of energy particles need to collide to make a reaction happen
• in an exothermic reaction, why does the products have less energy than the reactants

  energy has been transferred from the reaction to the surroundings
• what are some uses for an exothermic reaction in a day to day life


  hand warmers, self heating cans eg. for food or drink
• in an endothermic reaction, why do the products have more energy than the reactants

  energy has been taken in from the surroundings, the difference between the 2 shows how much energy has been taken in
• within a reaction profile of an endo and exo thermic reaction, whats 1 thing they have in common

  the energy rises to a peak, (activational energy)
• what is a chemical reaction example of a exothermic reaction

  oxidation and neutralisation
• what is a chemical reaction example of a endothermic reaction

  thermal decomposition
• define "bond energy"


  the energy needed to break the bonds between 2 atoms
• how do you calculate the energy change of a chemical reaction

  1.work out how much energy is needed to break the chemical bonds within the reaction

  2.work out how much energy is released when the new bonds are formed in the products