Question

What are the five signs of a chemical reaction \[?\]

Answer 1

Hint: Here first we know the chemical reaction is a process in which one or more substances (the reactants), are converted to one or more different substances (the products). Substances are either chemical elements or compounds.

Complete answer:
The signs of a chemical change are the following:
i) Formation of a precipitate
ii) Production of a gas
iii) Change in colour
iv) Energy change
v) Volume change

i) Formation of precipitate: A solid, known as a precipitate, that forms after two solutions are mixed. The precipitate will sometimes fall to the bottom of the container or it may remain suspended in the mixture and make the mixture cloudy.
An example is when magnesium and calcium oxides mix with water in plumbing and form deposits that clog the pipes.

ii) Production of gas: Gas bubbles appear after a chemical reaction has occurred and the mixture becomes saturated with gas.
An example is when an antacid is dropped in a glass of water and begins to bubble or when boiling water bubbles.

iii) Change in colour: Each chemical compound has a colour. When the compound changes during a chemical reaction, the colour may change as well. A colour change does not always indicate that a chemical change has occurred since there are other factors that can contribute to a change in colour.
An example is when a half-eaten apple turns brown after it has been exposed to the air.

iv) Energy change: Energy is required to break and form chemical bonds. Chemical reactions that involve bond-breaking tend to absorb energy from the surroundings, making the surroundings cooler. Chemical reactions that involve making bonds release energy, which makes the surroundings hotter. An example of a temperature change in a chemical reaction is when a burning fire produces heat.

v) Volume change: Each chemical compound has a specific density. If the chemical compound changes due to a chemical reaction, the density will also change. This causes the volume of the substance to recede or expand during the reaction process.
An example is when gas bubbles form in magma inside a volcano and expand too rapidly, leading to a volcanic eruption.

Note: Note that each chemical compound has its own distinct smell or taste. When the
compound changes after a chemical reaction, the taste or smell of the compound changes as well. An example of this is when fresh food that once smelled delicious slowly spoils and smells rotten. This bad smell sends a warning signal to the brain that tells the person not to eat the food.