What evidence can you observe that a reaction is taking place

What evidence can you observe that a reaction is taking place  

During a chemical reaction, reactants are consumed as new products are formed. Often, there are several telltale signs that a chemical reaction is taking place. 

Clean and dry the graduated cylinder, and then use it to measure 5.0 ml 0.01 AT sodium hydrogen sulfite solution (NaHS03). Slowly add this solution to the beaker while stirring with a stirring rod. 

Repeat Step 3 until the KMn04 solution in the beaker turns colorless. Stop adding the NaHS03 solution as soon as you obtain a colorless solution. Record your observations. 

Identify the evidence you observed that a chemical reaction was occurring. 

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