Does the application of heat to a substance always produce a chemical change?

Answer;

No, sometimes it just causes a physical change, such as ice melting to water.

Explanation;

-The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances in question; in a physical change there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition.

Heating a substance may cause a physical change or a chemical change.  For example melting ice to water, involves supplying heat to change ice into water which is a chemical change.

-On the other hand, an example of decomposition reactions are chemical reactions which involves supplying heat to a substance; for example decomposing copper (II) nitrate which yields, copper (ii) oxide, nitrogen (iv) oxide and oxygen gas, is chemical reaction.

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c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.