HKDSE Chemistry Question Review (20240703)

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#1 AAPL

02/07/24 18:01

Question: Which of the following process is endothermic?

A. Photosynthesis

B. Respiration

C. Combustion

D. Freezing

Hint: Note the definition of potential energy

#2 蕃茄伊貝二世

07/07/24 01:16

Solution:

B, C are obviously incorrect.

For D, when freezing, potential energy of the objectwill drop and is released as latent heat of fusion, so the process is actually exothermic.

The only correct option is A, as light energy from the surrounding is absorbed and converted to chemical energy stored in the starch formed.

#3 蕃茄伊貝二世

07/07/24 01:16

Solution:

B, C are obviously incorrect.

For D, when freezing, potential energy of the objectwill drop and is released as latent heat of fusion, so the process is actually exothermic.

The only correct option is A, as light energy from the surrounding is absorbed and converted to chemical energy stored in the starch formed.

potential energy of the object will drop

#4 蕃茄伊貝二世

07/07/24 01:19

Note that enthalpy = internal energy of a chemical. Since starch stores energy, it will release energy when burnt to form more stable products of lower enthalpy, i.e. carbon dioxide and water vapor.

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