Answer:
1. C
Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.
2. D
The speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time.
3. D
A reactant is a substance that is present at the start of a chemical reaction.
4. B
Concentration is the ratio of solute in a solution to either solvent or total solution.
5. D
Rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit time. ... For most reactions, the rate decreases as the reaction proceeds.
6. D
7. A
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