What is the change in mass and composition of catalyst after the completion of chemical reactions?

Answer

### Step-by-Step Solution:

1. **Definition of a Catalyst**: A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself.

2. **Role of a Catalyst in a Reaction**: During a chemical reaction, a catalyst provides an alternative pathway for the reaction to occur, which lowers the activation energy required for the reaction to proceed.

3. **Mass of the Catalyst**: After the completion of the chemical reaction, the mass of the catalyst remains unchanged. This means that the amount of catalyst present before the reaction is the same as that after the reaction.

4. **Composition of the Catalyst**: The composition of the catalyst also remains unchanged. This indicates that the chemical structure and properties of the catalyst do not alter during the reaction.

5. **Conclusion**: Therefore, both the mass and the composition of the catalyst remain unchanged after the completion of the chemical reactions.