A change is said to be a chemical change when

Options

A. energy changes occurs
B. new substances are formed
C. the change can not be easily reversed
D. all of these

Explanation

### Step-by-Step Solution:

1. **Understanding Changes**:
- There are two main types of changes: physical changes and chemical changes.
- Physical changes do not alter the chemical composition of a substance, while chemical changes do.

2. **Definition of Chemical Change**:
- A change is classified as a chemical change when a new substance is formed that has different properties and composition from the original substances (reactants).

3. **Characteristics of Chemical Changes**:
- **New Substances Formed**: In a chemical change, the reactants undergo a transformation to produce new substances. These new substances have different chemical and physical properties compared to the reactants.
- **Irreversibility**: Chemical changes are typically irreversible under normal conditions. This means that once a chemical change has occurred, the original substances cannot be easily recovered.
- **Energy Changes**: Chemical reactions often involve energy changes, such as the release or absorption of heat. This energy change is a driving force for the reaction.

4. **Conclusion**:
- A change is said to be a chemical change when:
- New substances with different properties are formed.
- The change is generally irreversible.
- There is an associated energy change during the reaction.

### Summary:
A change is classified as a chemical change when it results in the formation of new substances with different properties, is irreversible, and involves energy changes.

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