Question

Write a chemical equation that describes the melting of ice, and indicate whether \(\Delta H\) for the process is positive, negative, or zero. Under what temperature conditions does this process naturally occur?

Short answer

The melting of ice can be represented by the equation \(H_2O (s) \rightarrow H_2O (l)\). As this is an endothermic process, \(\Delta H\) is positive. This process naturally happens at temperatures above 0° Celsius or 273.15 Kelvin.

Step-by-step solution

Write the Chemical Equation

The chemical equation for the melting of ice is as follows: \ \[ H_2O (s) \rightarrow H_2O (l) \] This represents water in solid form (ice) transitioning to liquid form.

Indicate the Enthalpy Change (\(\Delta H\))

The melting process is an endothermic process, this means the system absorbs heat from the surroundings. Hence, the \(\Delta H\) for the process is positive. In other words, energy is required to break the bonds in the solid phase and convert it into a liquid phase.

State Under What Temperature Conditions the Process Occurs

Melting of ice naturally occurs at temperatures above 0 degrees Celsius (273.15 K). This is under 1 atmosphere of pressure conditions. The melting point could be affected by changes in pressure, but for standard conditions, the above holds true.

Key concepts

Chemical Equation

Understanding the chemical equation for the melting of ice is essential for grasping how substances change phases. A chemical equation represents the transformation of one or more substances into new substances, illustrating the reactants and products involved in the chemical process.

For the melting of ice, which is water in its solid form, the equation is simply expressed as: \[ H_2O (s) \rightarrow H_2O (l) \]Here,\( H_2O (s) \) represents ice, the solid form of water, and \( H_2O (l) \) is water in the liquid phase. This equation shows the phase transition without involving a change in the chemical composition – the molecules remain water molecules.

Enthalpy Change

Enthalpy change (\( \Delta H \)) is a measure of heat change during a chemical reaction at constant pressure. It indicates whether a process absorbs heat (endothermic) or releases heat (exothermic).

In the case of melting ice, the process is endothermic; heat energy is absorbed from the surroundings to overcome the molecular forces holding the solid structure together. Therefore, the \( \Delta H \) is positive, confirming the absorption of heat. Enthalpy is a vital concept in thermochemistry, as it helps us understand energy changes during phase transitions.

Endothermic Process

An endothermic process is characterized by the absorption of heat. This is in contrast with exothermic processes, which release heat into the surroundings.

Melting ice is a classic example of an endothermic reaction: it requires energy to move from solid to liquid form. The system, in this case the ice, absorbs thermal energy, which increases the motion of the water molecules, eventually overcoming the forces that keep them in a rigid structure. This is why we must supply heat to ice (like when we salt icy roads) to transition it to water.

Phase Transition

A phase transition is the transformation from one state of matter to another, such as solid to liquid or liquid to gas. Melting is one such transition, specifically from solid to liquid.

During the melting of ice, the phase transition occurs when the rigid, orderly structure of ice breaks down into the more random arrangement of water molecules in liquid form. Each molecule absorbs enough energy to break free from its position in the crystal lattice. This process is highly dependent on temperature and pressure conditions.

Melting Point

The melting point is the temperature at which a solid will begin to turn into a liquid. For pure, crystalline substances, this is a specific and characteristic temperature under a given pressure.

For ice, the melting point under normal atmospheric pressure (1 atmosphere) is at 0 degrees Celsius (273.15 Kelvin). This value can shift if the pressure changes, which is an aspect utilized in various applications, such as the production of synthetic diamonds. Yet for everyday scenarios, such as melting ice in drinks or ponds thawing in spring, it is the standard 0 degrees Celsius melting point that's relevant.