In which of the following cases can we be CERTAIN that a chemical change has taken place?
A)when a solid P is heated in a beaker for some time, it changes into a liquid.
B)when a liquid Q is taken in a beaker and powder R added to it and stirred, R dissolves in Q.
C)_when two liquids S and T are mixed, the beaker gets hot and a new liquid U is formed.
D)when a white powder V and black powder W are mixed, powder X with black and white particles is got.
Answers
option B on a broader range would include dissolution which is not a chemical change...
option A can include melting which also is not a chemical change
option D just includes mixing... (yeah u guessed it right!) which is also not a chemical change
On the other hand the release of heat is a major giveaway that a chemical reaction is taking place...
By the release of heat we can conclude that the substances that are mixed had a higher energy before the mixing and now they r achieving a more stable state thus releasing energy..... and the release of energy of a system to form a more stable component can be considered as a chemical reaction taking place.
Hope this helps
Question
A)when a solid P is heated in a beaker for some time, it changes into a liquid.
B)when a liquid Q is taken in a beaker and powder R added to it and stirred, R dissolves in Q.
C) When two liquids S and T are mixed, the beaker gets hot and a new liquid U is formed.
D)when a white powder V and black powder W are mixed, powder X with black and white particles is got.
Answer
option (c)
Reason
A) Here, only melting is taking place. Melting is a physical change, only.
B) Here, only dissolving is taking place, which is again not a chemical change.
C) Here , a new liquid is formed which is a chemical change. ( you can see the reason, which mentioned in the end of my answer)
D) Here, particles are only getting mixed , which is again not a chemical change.
Basic definition of chemical change (this can help you to solve these kind of questions)
Chemical reaction is a process in which one or more substances, the reactants, are converted to one or more different substances, the products. This change, leads to chemical change.