Silicon dioxide reacts with carbon to form silicon carbide and carbon monoxide as shown in the unbalanced reaction below. Determine the percent yield of silicon carbide if 79.1 grams of carbon reacts with an excess of silicon dioxide and 67.4 g of silicon carbide is actually recovered. SiO2 + C → SiC + CO

Excess silicon dioxide" tells us carbon is the limiting reactant, and thus the amount of silicon carbide produced depends on how much carbon is available to react.
*Based on the balanced equation, for every 3 moles carbon reacted, 1 mole silicon carbide is produced.
*Molar mass carbon: 12.01 g/mol
*Molar mass silicon carbide: 28.09 g + 12.01 g = 40.1 g/mol

79.1 g carbon x (1 mol carbon / 12.01 g carbon) x (1 mol silicon carbide / 3 mol carbon) x (40.1 g silicon carbide / 1 mol silicon carbide) = 88.04 g silicon carbide

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