What is the indication of completion of reaction is this experiment?

How do you know a chemical reaction has taken place?

For which of the following cases is there a clear indication that a chemical reaction is taking place?Case 1:  Two clear, colorless liquids at 19.5 degrees Celsius are combined in a test tube.  A few seconds later, the contents of the test tube appear to be a clear, colorless liquid with a temperature of 19.8 degrees Celsius.Case 2:  Two clear, colorless liquids at 24.3 degrees Celsius are combined in a test tube.  A few seconds later, the contents of the test tube appear to be a clear, colorless liquid with a temperature of 32.9 degrees Celsius.

99% of a first order reaction, was completed in 32 minute. When will 99.9% of the reaction complete?

A student observes several reactions. Describe one observation the student might make that would indicate a chemical reaction has taken place.

In which of the following case, does the reaction go fartiest to completion ifKc=102Kc=10Kc=10−2Kc=1