Explain the observed temperature change upon mixing ethanol and cyclohexane.
When ethanol (C2H5OH) and cyclohexane (C6H12) are mixed together, an observed temperature change can occur. This temperature change is primarily due to the difference in intermolecular forces between these two substances.
To understand the observed temperature change, let's consider the intermolecular forces present in each substance.
Ethanol is a polar molecule since it contains an oxygen atom bonded to a hydrogen atom (OH group). These polar groups give ethanol its ability to form hydrogen bonds with other ethanol molecules. Hydrogen bonding is a strong intermolecular force that results from the partial positive charge on hydrogen bonding with the partial negative charge on another atom.
Cyclohexane, on the other hand, is a nonpolar molecule. It consists of carbon and hydrogen atoms arranged in a ring structure, lacking any significant charge separation.
When ethanol and cyclohexane are mixed together, their molecules intermingle and interact with each other. This mixing results in the breaking of the original intermolecular forces in both substances and the formation of new intermolecular forces.
The observed temperature change can occur due to two main factors:
1. Energy required to break intermolecular forces: To mix ethanol and cyclohexane, the original intermolecular forces between ethanol molecules and between cyclohexane molecules need to be broken. Breaking these forces requires energy, which is absorbed from the surroundings, causing a decrease in temperature. This process is an endothermic reaction.
2. Energy released in the formation of new intermolecular forces: As the ethanol and cyclohexane molecules mix, new intermolecular forces between ethanol and cyclohexane molecules are formed. In this case, the new intermolecular forces are primarily London dispersion forces, which exist between all molecules and result from temporary shifts in electron density. The formation of these new intermolecular forces releases energy, which is gained from the surroundings and causes an increase in temperature. This process is an exothermic reaction.
The net temperature change upon mixing ethanol and cyclohexane depends on the balance between the energy required to break the original intermolecular forces and the energy released in the formation of new intermolecular forces. If the energy released in the formation of new intermolecular forces is greater than the energy required to break the original forces, the overall process will be exothermic and result in a temperature increase. Conversely, if the energy required to break the original forces is greater, the overall process will be endothermic and result in a temperature decrease.
To precisely determine the observed temperature change, one would need to measure the initial temperatures of the pure substances, carefully mix them, and continuously monitor and record the temperature changes during the mixing process using a thermometer or a calorimeter.