Reversible reactions and equilibriumIB MYP Chemistry: Flashcards

Exam questions on Reversible reactions and equilibrium

1. A technician in a school laboratory in Nairobi heats blue crystals of hydrated copper(II) sulfate in a test tube. The crystals turn into a white powder and water vapour condenses near the top of the tube. When the tube has cooled, she adds a few drops of water to the white powder. It turns blue again and the tube feels warm.
   Describe what is meant by a reversible reaction, using this experiment as an example.2 marks
2. A student seals brown nitrogen dioxide gas, NO₂, in a glass tube kept at a constant temperature. Over several minutes some of the brown gas changes into colourless dinitrogen tetroxide, N₂O₄, as shown by the equation 2NO₂(g) ⇌ N₂O₄(g). After ten minutes the colour stops getting paler and stays the same shade of brown, although both gases are still present.
   Explain why the colour of the gas mixture stays the same even though the reactions have not stopped.2 marks
3. A group of students in a school in Singapore investigate how temperature affects the equilibrium 2NO₂(g) ⇌ N₂O₄(g). NO₂ is a dark brown gas and N₂O₄ is colourless. The forward reaction is exothermic. They seal the same mixture of the gases in three identical tubes and place one tube in a beaker of ice water, one in a beaker of water at room temperature and one in a beaker of water at about 80 °C. After ten minutes the tube in ice water is pale brown, the tube at room temperature is medium brown and the tube in hot water is dark brown.
   Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks