Final answer:
Excessive heat can negatively affect fractional distillation by causing decomposition and unwanted reactions, making separation difficult, and resulting in loss of yield.
Step-by-step explanation:
Excessive heat can affect fractional distillation in several ways. Firstly, if the heat is too high, it can cause the components to decompose or react with each other, leading to unwanted chemical reactions and the formation of byproducts. Secondly, excessive heat can cause the lighter, lower-boiling components to evaporate too quickly, making it difficult to separate them properly. Lastly, the use of excessive heat can also result in loss of yield, as some of the desired components may be lost or destroyed due to the high temperatures.