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Endothermic and Exothermic Reactions

AIM:                                                                                                                   

Investigate Endo- and Exothermic reactions and to know where we use these reactions in the world every day.

HOW DOES IT WORK?                                                                       

Time Allocation: 45 Min

Chemical reactions can be classified as exothermic or endothermic, depending on the temperature change of the mixture during the reaction. Learners have to conduct a number of experiments to determine which of them are exothermic – temperature increases- and which are endothermic – temperature decreases.

Due to the great number of gases on earth, it is impossible to describe the behaviour of each gas on its own. To simplify this task, scientists decided to create an imaginary gas which is an approximation of the behaviour of all real gases on earth – this gas is called an ideal gas. Real gasses show the behaviour of ideal gases under normal temperatures and pressures, but deviate from ideal gas behaviour at very low temperatures and high pressures.

 

APPARATUS:

  • 2 x Test tube racks
  • 12 test tubes
  • Thermometer 150 mm
  • Spatula
  • Stirring rod 150 mm
  • Pair of Forceps
  • 2 x Beakers 250ml
  • Water bowl
  • Mortar and pestle
  • Potassium nitrate (KNO3(s))
  • Potassium bromide (KBr(s))
  • Magnesium sulphate (MgSO4(s))
  • Ammonium nitrate (NH4NO3(s))
  • Ammonium hydroxide (H4OH(s))
  • Barium chloride (BaCℓ2(s))
  • Citric acid (C6H8O7(s))
  • Vinegar (CH3COOH (aq))
  • Sodium carbonate (Na2CO3(s))
  • Sodium hydrogen carbonate (NaHCO3(s))
  • Sodium thiosulphate (Na2S2O3(s))
  • Potassium permanganate (KMnO4(s))
  • Copper(II)sulphate (CuSO4(s))
  • Lithium (Li(s))
  • Magnesium ribbon (Mg(s))
  • Magnesium powder (Mg(s))
  • Dilute sulphur acid (H2SO4(aq))
  • Calcium chloride (CaCℓ2(s)
  • Glycerine (C6H8O7(ℓ))
  • Distilled water
  • Cal-C-Vita tablet.

METHOD:

Experiment 1: Lithium and Water Reaction
  • Fill a beaker with distilled water and measure the temperature.
  • Use the pair of forceps to place a small piece of lithium in the water.
  • Write down all the observations.
  • Measure the change in temperature.
Experiment 2: Sulphuric Acid and Water Reaction
  • Fill a test tube half to its volume with distilled water and measure the temperature of the water.
  • Carefully add H2SO4(ℓ) in small amounts to the water while stirring.
  • Measure the change in temperature.
Experiment 3: Dissolution of salts in water Reaction
  • Fill six test tubes with distilled water to half their volume.
  • Measure the temperature of the water.
  • Add a spatula full of each of the following salts to a different test tube with water: KNO3(s), KBr(s), NH4NO3(s), Na2S2O3(s), CaC 2(s) and a Cal-C-Vita tablet.
  • Stir the solutions to dissolve the salt.
  • Measure and record the change in temperature of the solution.
Experiment 4: Acid-carbonate reactions Reaction
  • Fill a test tube to a third of its volume with distilled water.
  • Add a half spatula full of citric acid to the water in the test tube and stir until dissolved.
  • Fill a second test tube with vinegar to a third of its volume.
  • Measure the temperature of the content of the two test tubes.
  • Add a spatula full of NaHCO3(s) to the citric acid solution.
  • Measure the change in temperature during the process.
  • Add a spatula full of Na2CO3(s) to the vinegar,
  • Measure the change in temperature during the process.
Experiment 5: Potassium permanganate and glycerol Reaction
  • Grind a small amount (three spatulas full) of KMnO4(s) in the mortar and pestle and transfer to a glass beaker (or any other suitable container).
  • Carefully add a few drops of C6H8O7( ) to the crystals.
  • Record the observations.
Experiment 6: Copper(II)sulphate Reaction                              
  • Put a thermometer in a test tube.
  • Cover the bulb with anhydrous CuSO4(s).
  • Add water drop by drop and record the change in temperature.
  • Prepare a concentrated solution of CuSO4(aq) and fill two test tubes to a third of its volume with the solution.
  • Add a spatula full of Mg(s) (in powder form) to the one solution and a number of pieces of Mg(s) (ribbon) to the second solution.
  • Record the temperature changes.

PRECAUTIONS:

  • Wear safety clothing while the experiments are done.
  • Wear safety goggles.
  • Use strengthened glassware.
  • Avoid skin contact with any chemicals.
  • Lithium is stored under paraffin because it reacts spontaneously with O2(g) and H2O(ℓ).
  • Do not touch it with bare hands – use tweezers.
  • H2SO4(ℓ) is hazardous. It causes severe burns and reacts violently, becoming very hot, when mixed with water.
  • It can also irritate the eyes and skin.
  • Add the acid drop by drop to the water and not vice versa.
  • The reaction between potassium permanganate and glycerine is dangerous, because KMnO4(s) is a strong reducing agent – Take care when conducting the experiment!