For each of the following, identify whether a chemical change has occurred, and explain your answer.

  • Two colourless solutions at room temperature are mixed. After a minute, the temperature of the mixture is 60˚C. 
  • Ice is taken from the freezer and left on the beach. The temperature rises from 0˚C to 20˚C and the ice melts.
  • Yellow sulfur powder and iron fillings are heated in a crucible. After heating, only a black solid remains. 
  • Expert Answers

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    It is generally termed as when a substance came into contact with another substance and then another substance is produced. Chemical change is accompanied by series of evidence that can be noticed in a system. Some of its apparent evidences are change of the state of the matter, production/release of a gas, new odor, formation of precipitate, change in colour, disappearance of substance, increase in temperature and violent/explosive reaction.

    In this connection, single evidence may or may not be sufficient.

    1. Temperature increase shows that there has been a chemical change.

    2. Ice melts at temperature higher than 0 degrees Celsius. Melting and freezing are physical changes. 

    3. Two things happen in the crucible: Disappearance of the reactants, formation of new substance after heating. 

     

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