Which set of procedures and observations indicates a chemical change?
(1) ethanol is added to an empty beaker and the ethanol eventually disappears.
(2) a solid is gently heated in a crucible and the solid slowly turns to liquid.
(3) large crystals are crushed with a mortar and pestle and become powder.
(4) a cool, shiny metal is added to water in a beaker and rapid bubbling occurs.

Option 4 seems to be the one undergoing a chemical change because there is a formation gas from the bubbling that occurs. Chemical change is the change that results to the formation of a new substance. The other options given are examples of physical change.

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic