Chemistry practical for grade 8 9

1. Endothermic and Exothermic Reactions Experiment
Every chemical reaction that exists is one of two things: endothermic or exothermic. The Greek
root therm means temperature or heat, which gives us a clue about all reactions: there is energy
exchange! Endo means "within" while exo means "outside," so these types of reactions are
opposite.
Endothermic reactions are those which absorb heat during the reaction. They take in more energy
than they give off, which leaves the surroundings cooler than the starting point. Evaporation of
water by sunlight is a great example. The sun and the liquid water combine and the water absorbs
energy and eventually becomes as gas.
Exothermic reactions are exactly the opposite. While they take some energy to get going, called
the activation energy of reaction, these reactions give off heat during the reaction. Good
examples of exothermic reactions are explosions like fireworks or combustion in engines.
Problem:
Observe endothermic and exothermic reactions and determine which absorb or produce the most
energy. Which reactions will be endothermic? Which reactions will be exothermic? Why?
Materials
 Clear glass or cup
 Water
 White vinegar
 Baking Soda
 Magnesium ribbon
 Hydrogen peroxide
 Potassium Chloride
 Manganese oxide
 Hydrochloric acid
 Thermometer
Procedure
1. The table below has a list of liquids to combine with solids. Pick a combination, and fill
the glass or cup about half way with the liquid.
2. Insert the thermometer in the liquid and record the temperature.
3. Add a tablespoon of the dry material. Record your observations.
4. Wait 2 minutes and record the final temperature of the solution. Why should you wait the
same amount of time for each trial?
5. Discard the solution and try another combination.

2. 6. For each trial, calculate the change in temperature of the reaction by subtracting the final
value from the initial value.
Try any of these combinations:
Liquid Additive
Water Ice
Vinegar Baking soda
Potassium Chloride Water
Hydrogen Peroxide Manganese oxide
Magnesium ribbon Hydrochloric acid
Results
Endothermic reactions: water and Epsom salt, water and NoSalt, water and ice
Exothermic reactions: vinegar and baking soda, vinegar and steel wool, hydrogen peroxide and
dry yeast, acetone and Styrofoam
Graph your results! Make a bar for each reaction and draw a line from 0 to the temperature
change. Be sure to label each line!
Why?
Energy can be a reactant or byproduct of any reaction. While all reactions require some amount
of energy to get going, called the activation energy, whether the reaction is endothermic or
exothermic depends on where energy fits into the equation. For example:
Endothermic reactions:
reactants + energy = products
And for Exothermic reactions:
reactants = products + energy
It is important to measure the time for each experiment because some may go on even longer
than 2 minutes, or be done far before 2 minutes have passed. Taking the temperature
measurements at the same time for each trial allows you to compare the combinations. Time is
the control variable.
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