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Which of the following statements is true?

A.
Chemical reactions can only absorb thermal energy.
B.
Chemical reactions can neither absorb thermal energy nor release thermal energy.
C.
Chemical reactions can either absorb thermal energy or release thermal energy.
D.
Chemical reactions can only release thermal energy.

User Ddcruver
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1 Answer

5 votes

Answer: C. Chemical reaction absorb or release thermal (and sometimes other) energy

Step-by-step explanation:

Chemical reactions can result in products with more or less chemical energy than the precursors. When products have less chemical energy, the excess is converted to heat (exothermic reaction)

When the products have more chemical energy, heat must be added to make up the difference (Endothermic reaction)

Fireworks are examples of exothermic reactions where the excess is released as thermal, mechanical, and radiant energy. A lit match releases thermal and radiant energy.

Respiration is also an exothermic reaction

C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy

Respiration is the reverse of photosynthesis, an endothermic process. The overall photosynthetic reaction is 6CO2 + 6H2O + energy —> 6C6H12O6 + 6O2

In this case radiant energy drives the reaction.

The reaction 2H2O —> 2H2 + O2 is an endothermic reaction driven by electrical energy.

Many reactions are reversible and if one is endothermic, the reverse is exothermic e.g. 2H2 + O2 —> 2H2O +energy is the reverse of electrolysis of water, or respiration vs photosynthesis.

User Shatiz
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