What evidence of a chemical reaction might you see in the following cases?

1. Dropping an Alka-Seltzer tablet into a glass of water





2. Bleaching a stain





3. Burning a match








4. Rusting of an iron nail





I'm not sure if I got #1 right. I answer, It reacts to produce bubbles of carbon dioxide and soluble salts.What evidence of a chemical reaction might you see in the following cases?
You are correct that gases are formed for example #1 but I don't think that is the desired answer. I arrived to that conclusion based on the fact that each of the four examples above requires knowledge that goes beyond just chemical reactions.





For instance, in example #1, you would need to know what an ';Alka-Seltzer tablet'; is. You would need to know that these tablets contain bicarbonates and citric acid to know that CO2 would form when dropped into water.





The tablet doesn't react with the water. It is dissolved in the water where it allows the sodium bicarbonate and citric acid that is in the tablet to react.





All chemical reactions either gives off heat (exothermic) or needs heat (endothermic).





So if you want to know if a chemical reaction took place, take a temperature reading.





All four above are examples of exothermic reactions.





Color changes. Check for any color changes, too. Three of the four examples would exhibit color changes (e.g. rusting nail).





Changes in weight. For instance, the burning match would weigh less over time as more and more of it is converted to waste products of carbon dioxide and water vapor. Iron weighs less than Iron Oxide.What evidence of a chemical reaction might you see in the following cases?
2. is an oxidation reaction.


3. carbon and hydrogen in wood of match is burned to make co2, h2o.


4. formation of iron oxide (reaction of iron with oxygen in air)