Chemical Energetics: Physical and Chemical Changes

CHAPTER 7- CHEMICAL ENERGETICS: Physical and Chemical Changes

Based on the material provided, the study of matter involves understanding the fundamental differences between physical and chemical changes. These changes are defined by whether or not the internal composition of a substance is altered during a process.

Physical Change: Definitions and Defining Characteristics

A physical change is defined as a change in which only the physical properties. OF a substance change. This denotes that the identifying characteristics of the substance are preserved even if its external form is modified.

Major Features of Physical Changes

The text identifies four major features that characterize a physical change:

1. No new Substance produced: The process does not result in the creation of a different kind of matter.

2. Chemical composition remains unchanged: The molecular structure and internal makeup of the material do not alter.

3. Usually reversible: These changes can typically be undone to restore the substance to its original form.

4. Change in physical properties: These transitions are limited to changes in ( state, size, shape, appearance ).

Elaborative Examples and Explanations of Physical Changes

The transcript lists several practical examples of physical changes:

• Melting of ice into water

• Boiling of water

• Dissolving sugar into water

• Cutting paper into pieces

• Stretching a rubber band

To further clarify the nature of these transformations, the material explains that when ice melts into water, it's still $H_2O$. Only the State of matter changes, not the substance itself. This reinforces the principle that while the arrangement of the molecules or the phase may change, the identity of the substance ($H_2O$) is constant.

Chemical Change: Definitions and Defining Characteristics

A chemical change is defined as a change in which. one Dr more new substances. With different chemical properties are formed. This type of change results in a transformation where the ending material is chemically distinct from the starting material.

Major Features of Chemical Changes

The major features of chemical changes include:

1. Formation of new substances: Transition where substance (5) formed.

2. Chemical composition changes: The underlying atomic structure and chemical identity of the matter is rearranged.

3. Usually irreversible: Once the reaction occurs, it is generally not possible to return to the original substances.

4. Energy emission: Energy is given out in the form of heat and light-.

5. Bonding changes: The process Involves breaking and forming of chemical bonds-.

Examples of Chemical Processes and Reactions

The material identifies several specific occurrences that qualify as chemical changes:

• Rusting of iron

• Burning of wood or paper

• Digestion of food

• Reaction bin acid and base

• Curdling of milk

• Ripening of fruits

In each of these instances, the original substance undergoes a fundamental chemical transformation, creating new products with entirely different properties.