Explain why an ice cube melting would not be an example of a chemical reaction

How are isotopes of the same chemical element alike? how are they different?

8. what happens to matter during a chemical reaction

At a certain temperature the rate of this reaction is first order in hi with a rate constant of : 0.0632s2hig=h2g+i2g suppose a vessel contains hi at a concentration of 1.28m . calculate how long it takes for the concentration of hi to decrease to 17.0% of its initial value. you may assume no other reaction is important. round your answer to 2 significant digits.