1. Define the term "enthalpy change" and provide an example of an endothermic reaction. Answer: Enthalpy change is the heat change at constant pressure. An example of an endothermic reaction is the melting of ice. 2. Explain the concept of entropy and its significance in spontaneous reactions. Answer: Entropy is a measure of the disorder or randomness in a system. Spontaneous reactions often lead to an increase in entropy. 3. Describe the process of fractional distillation and its application in separating organic compounds. Answer: Fractional distillation is a technique used to separate mixtures of liquids based on differences in their boiling points. It is commonly used in the petroleum industry to separate crude oil into its components. 4. What is the principle behind chromatography, and how is it used to identify substances? Answer: Chromatography separates components of a mixture based on their different interactions with a stationary phase and a mobile phase. It is used to identify substances by comparing retention times or Rf values.