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Understanding Chemical
Reactions
Bonds & Energy
Basic Revision




For a chemical reaction to occur, bonds
must be both formed and broken
Fe + CuSO4

Cu

+ FeSO4
Basic Revision




Chemical reactions always involve energy
changes.
Making and breaking bonds involves
energy changes
ENERGY AND CHEMICAL
REACTIONS
Exothermic reactions
 These reactions give out heat energy.
 Combustion is an exothermic r...
ENERGY AND CHEMICAL
REACTIONS
Endothermic reactions
 These reactions take in heat energy from
their surroundings.
 These...
ENERGY AND CHEMICAL
REACTIONS






Use the apparatus as
shown.
Work with 20ml of
each substance in
turn.
Copy the resu...
RISK ASSESSMENT






You will be using acids so wear safety
goggles.
Wipe up spills immediately
Replace stoppers
Do n...
ENERGY AND CHEMICAL
REACTIONS
Reaction

sodium hydroxide sol’n +
hydrochloric acid
sodium hydrogen carbonate
sol’n + citri...
ENERGY LEVEL DIAGRAMS




We can show the energy transfers in
reactions on an energy level diagram.
These show us the en...
Exothermic energy level diagram
Exothermic energy level diagram






∆H (‘delta H’) is the
symbol for the ‘change in
energy’.
In an exothermic reactio...
Endothermic energy level diagram
Endoothermic energy level diagram




In an endothermic
reaction the products
have more energy
than the reactants.
∆H is...
Making and breaking bonds




We have seen how bonds are formed
(both ionic and covalent)
Do you think energy is needed ...


Breaking bonds requires energy. It
is endothermic.




Breaking bonds requires energy. It
is endothermic.
Making new bonds gives out
energy. It is exothermic.
Bonds and energy
Bonds and energy
Bonds and energy
Bonds and energy
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Transcript of "Bonds and energy"

  1. 1. Understanding Chemical Reactions Bonds & Energy
  2. 2. Basic Revision   For a chemical reaction to occur, bonds must be both formed and broken Fe + CuSO4 Cu + FeSO4
  3. 3. Basic Revision   Chemical reactions always involve energy changes. Making and breaking bonds involves energy changes
  4. 4. ENERGY AND CHEMICAL REACTIONS Exothermic reactions  These reactions give out heat energy.  Combustion is an exothermic reaction.
  5. 5. ENERGY AND CHEMICAL REACTIONS Endothermic reactions  These reactions take in heat energy from their surroundings.  These cause temperatures to fall.
  6. 6. ENERGY AND CHEMICAL REACTIONS    Use the apparatus as shown. Work with 20ml of each substance in turn. Copy the results table before you start
  7. 7. RISK ASSESSMENT     You will be using acids so wear safety goggles. Wipe up spills immediately Replace stoppers Do not put solids down the sink – use the bowl at the front!
  8. 8. ENERGY AND CHEMICAL REACTIONS Reaction sodium hydroxide sol’n + hydrochloric acid sodium hydrogen carbonate sol’n + citric acid copper sulphate sol’n + magnesium powder sulphuric acid + magnesium ribbon barium chloride + sodium sulphate temp. temp. before after mixing ( 0 C) mixing ( 0 C) Exothermic or Endothermic?
  9. 9. ENERGY LEVEL DIAGRAMS   We can show the energy transfers in reactions on an energy level diagram. These show us the energy stored in the reactants compared to the energy stored in the products.
  10. 10. Exothermic energy level diagram
  11. 11. Exothermic energy level diagram    ∆H (‘delta H’) is the symbol for the ‘change in energy’. In an exothermic reaction the products have less energy than the reactants. ∆H is negative for an exothermic reaction.
  12. 12. Endothermic energy level diagram
  13. 13. Endoothermic energy level diagram   In an endothermic reaction the products have more energy than the reactants. ∆H is positive for an endothermic reaction.
  14. 14. Making and breaking bonds   We have seen how bonds are formed (both ionic and covalent) Do you think energy is needed to break bonds?
  15. 15.  Breaking bonds requires energy. It is endothermic.
  16. 16.   Breaking bonds requires energy. It is endothermic. Making new bonds gives out energy. It is exothermic.
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