In the following list, only is not an example of a chemical reaction.

a) burning a plastic water bottle

b) the production of hydrogen gas from water

c) the tarnishing of a copper penny

d) chopping a log into sawdust

e) charging a cellular phone

Thus chopping a log into sawdust is not an example of a chemical reaction.

Explanation:

Physical reaction is a reaction in which there is no rearrangement of atoms and thus no new substance is formed. There is only change in physical state of the substance.

Example: chopping a log into sawdust as the shape and size of wood changes.

Chemical reaction is a reaction in which there is rearrangement of atoms and thus new substance is formed. There may or may not be a change in physical state.

Example: burning a plastic water bottle : as the plastic would combine with oxygen to give oxidised products.

the production of hydrogen gas from water: the chemical composition changes

the tarnishing of a copper penny: oxidation of copper takes place to give copper oxide.

charging a cellular phone: the electrical energy is used for a chemical reaction

r just means there's a number of carbon in teh chain. for example rcooh means that after x number of carbon, the chain ends with cooh.

explanation:

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.