Question

A person packs two identical coolers for a picnic, placing twenty-four 12-ounce soft drinks and 5 pounds of ice in each. However, the drinks put into cooler A were refrigerated for several hours before they were packed in the cooler, while the drinks put into cooler B were at room temperature. When the picnickers open the two coolers 3 hours later, most of the ice in cooler A is still present, while nearly all of the ice in cooler B has melted. Explain this difference.

Short answer

Cooler A's drinks were refrigerated, so they were already cool and absorbed less heat from the ice, causing less ice to melt. Cooler B's room temperature drinks absorbed more heat from the ice to reach thermal equilibrium, resulting in more ice melting.

Step-by-step solution

- Understanding Heat Transfer

The difference in ice melting can be explained by the concept of heat transfer. Warmer objects will transfer heat to cooler objects until thermal equilibrium is reached. Since the drinks in cooler A were refrigerated, they were already at a low temperature, which means they would absorb less heat from the ice, resulting in less ice melting.

- Thermal Equilibrium

Thermal equilibrium occurs when two objects have reached the same temperature and there is no further heat transfer between them. Since the drinks in cooler B were at room temperature, which is higher than the temperature of the ice, they would absorb more heat from the ice until both the drinks and the remaining ice reached the same temperature, thus more ice melted in cooler B.

- Specific Heat Capacity

Specific heat capacity is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The drinks at room temperature in cooler B would have a higher heat capacity compared to the refrigerated drinks in cooler A, meaning they can store more heat energy, which would be drawn from the ice, causing it to melt faster.

Key concepts

Thermal Equilibrium

Understanding thermal equilibrium is crucial when explaining heat transfer in chemistry, particularly in scenarios like why ice melts differently in two coolers with drinks at varying temperatures. Thermal equilibrium is defined as the condition where two or more objects in contact with each other reach the same temperature, and as a result, no further heat flows between them.

When you place a cold drink next to ice, heat from the warmer drink will naturally flow to the colder ice until both substances reach the same temperature. This process continues until equilibrium is achieved, which is why cooler A, with chilled drinks, retained more ice than cooler B, where the drinks were initially at room temperature. The phenomenon also underscores why insulating materials are vital in coolers to minimize unwanted heat transfer with the external environment, keeping the contents at your desired temperature for longer periods.

Specific Heat Capacity

The term 'specific heat capacity' might sound intimidating, but it's a straightforward concept that explains a lot about everyday phenomena, like why different substances warm up at different rates. Specific heat capacity is a material's ability to hold heat energy. To put it simply, it's the measure of the amount of heat energy needed to raise the temperature of one gram of a substance by one degree Celsius.

Picture two objects – one can soak up a lot of heat before it starts to get warm, while the other starts to heat up almost immediately. The first object has a higher specific heat capacity. This is why the drinks in cooler B, with a higher specific heat capacity at room temperature, absorbed more energy from the ice and resulted in more ice melting. It also helps to explain why certain materials are better at keeping things cool (or warm), depending on their specific heat capacities.

Temperature and Heat Relation

People often use the terms 'temperature' and 'heat' interchangeably, but in chemistry, they have distinct meanings. Temperature is a measure of how hot or cold something is, technically the measure of the average kinetic energy of the particles in an object. Heat, on the other hand, refers to the transfer of thermal energy from one thing to another.

A higher temperature object doesn’t always mean it contains more heat, as this depends on mass and specific heat capacity. For instance, a large volume of water at a lower temperature can contain more heat than a small metal rod at a higher temperature. When the non-refrigerated drinks at a higher temperature in cooler B were placed with the ice, the transfer of heat from the drinks to the ice accumulated until both reached the same temperature, leading to the ice's melting. Understanding this relationship is essential in practical applications, such as designing thermal systems or even packing for your next picnic.