Chapter 6 suggested solutions
Solutions for Chapter 6
When water is boiled in a teakettle, no chemical reaction occurs.
There is a physical change
When boiling water is poured into a bowl containing a package of instant oatmeal and
stirred to make a hot cereal breakfast, various components of the cereal dissolve or are re-
hydrated (the oatmeal had been previously prepared and the chemical changes that make
oatmeal from oat flakes had occurred and then water was removed to produce the instant
product). The changes occurring when the product is re-hydrated are probably reasonably
classified as physical, not chemical changes.
When a glass of a carbonated soft drink is left overnight and tastes “flat” the next morning,
dissolved in the soft drink as CO
has escaped to the atmosphere. You might think
of this as a physical reaction, but it can also be considered a chemical reaction, if some of the
dissolved carbon dioxide was present as carbonic acid, (HO)
, which is a different
When a glass of ice cubes and water is left overnight and there are no ice cubes in the water
the next morning, no chemical reaction has occurred. The ice cubes melted, H
but no new chemical species formed.
When a match is dropped on the floor, no chemical change (reaction) occurs. The match is
still the match.
When a match is struck and used to start a barbeque, several chemical reactions occur. There
is a chemical reaction that uses the energy of the friction of the match head to initiate the
reaction that lights the match (which continues to burn because the energy released in the
burning sustains the reactions). Once the match is burning, the flame is used to start the
chemical reaction in the charcoal, propane, or other fuel used in the barbeque. In both cases, the
products of the change, carbon dioxide, water, ashes, and so on, are different chemical species
than were present in the match and fuel.
When a piece of paper is folded to make a paper airplane, no chemical change (reaction)
occurs. The paper is still the paper.
When a piece of paper is torn into many small pieces to make confetti, you can argue that no
chemical change (reaction) has occurred because the little pieces are still paper. On the other
hand, tearing the paper apart breaks a large number on intermolecular (not covalent) bonds
between the cellulose polymer molecules that make up the paper, so many of these molecules
are not making the same bonding interactions they were previously. The distinction between
chemical change and physical change is sometimes quite fuzzy and probably not worth making.
When an acorn buried and forgotten by a squirrel grows into an oak tree, a very large
chemical reactions have occurred. Many compounds not originally present in the
acorn are now present in the oak tree. Other compounds that were originally present in the acorn