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...

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

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

Asked on by al0987

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jerichorayel's profile pic

jerichorayel | College Teacher | (Level 2) Senior Educator

Posted on

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. 

 

radwolfsdragon's profile pic

radwolfsdragon | Student, Undergraduate | eNotes Newbie

Posted on

For the first one, a chemical change has indeed occured. Reason is that the two colourless solutions have undergone an exothermic reaction. Thus releasing energy in form of heat to the surrounding. the molecules of the solutions are forming chemical bonds with each other and in doing so they release energy. For the second one, there is no chemical change but rather a physical change. the ice melting on the beach due to the high temperatures is a physical change because the ice is changing state from solid to liquid and this is a reversible change. for the third one, there is a chemical change. the yellow sulphur powder reacted with the iron fillings to form iron (ii) sulphide which is a black solid and black is the colour of all sulphides.

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