ppt on energetics

1. 7.1 ENDOTHERMIC & EXOTHERMIC
OBJECTIVES:
To explain the terms endothermic and exothermic
To give examples of reactions for each
STARTER:
What do we mean by the
terms endothermic and
exothermic?
Can you give any examples of
each?
KEY WORDS:
ENDOTHERMIC
EXOTHERMIC
ENTHALPY
THERMOCHEMISTRY

2. Chemical reactions can either release energy to
their surroundings, __________, or energy can be
transferred to them from the surroundings,
____________.
EXOTHERMIC
ENDOTHERMIC
KEY IDEA
Bonds contain energy. You need to put in energy to
break bonds apart in the REACTANTS in a chemical
reaction. Energy is released when new bonds form in the
PRODUCTS in a chemical reaction. When bonds break,
energy is absorbed (endothermic). When bonds form,
energy is released (exothermic).
7.1 ENDOTHERMIC & EXOTHERMIC
http://www.youtube.com/watch?v=p-
27I_osoaw

3. 7.1 ENDOTHERMIC & EXOTHERMIC
EXAMPLES:
Exothermic:
• Neutralising an acid with an alkali
• Burning magnesium
• Adding water to anhydrous copper sulphate
Endothermic:
• Thermal decomposition of limestone
• Photosynthesis
• Heating blue copper sulphate
A reaction endothermic in one
direction is always exothermic
in the other

4. 7.1 ENDOTHERMIC & EXOTHERMIC
QUANTITIES:
• Energy is measured in kilojoules per mole
• kJmol-1
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (l)
• Combustion of methane  one mole of methane reacts
with 2 moles of oxygen
• It gives out 890kJ of energy

5. 7.1 ENDOTHERMIC & EXOTHERMIC
INVESTIGATION
Follow the instructions on the handout and then answer the
following questions:
1. The first reaction is between an acid and an alkali, what do we call
this type of reaction?
2. Which gas is given off when sodium hydrogen carbonate reacts with
citric acid?
3. Which type of reaction takes place between copper (II) sulfate and
magnesium?
4. Which reactions are exothermic and which are endothermic?
5. Describe in terms of bond breaking and bond making, why some
reactions are exothermic and some are endothermic.

6. 7.1 ENDOTHERMIC & EXOTHERMIC
INVESTIGATION
1. Heat some blue copper sulphate in a boiling tube
2. Let it cool
3. Add a couple of drops of water and feel the bottom of
the boiling tube
4. Write out an equation for the reaction
5. Which way is endothermic which is exothermic? How do
you know?

7. 7.1 ENDOTHERMIC & EXOTHERMIC
ANSWERS
1. Neutralisation.
2. Carbon dioxide.
3. Displacement reaction – magnesium is higher in the reactivity series
so it displaces copper from its sulphate.
4. Sodium hydrogen carbonate solution + citric acid is endothermic, the
other reactions are exothermic.
5. Reactions involve making and breaking bonds. Energy is required to
break bonds. Energy is released when bonds are made. If more
energy is required to break the bonds in a reaction than that
released by making the bonds then the reaction is endothermic
(heat is absorbed). If less energy is required to break the bonds
than that released by making the bonds then the reaction is
exothermic (heat is produced).

8. I CAN…I AM…
How low can you go?? Write what you can do and what
grade this is  show some proof you can do this!
I CAN… I AM…
Describe the terms endothermic and
exothermic
C
Give examples of endothermic and exothermic
reactions
B
Explain endothermic and exothermic reactions
using ideas of bond energy
A