Final answer:
A change in supply/demand involves shifts of the supply or demand curve and is caused by factors affecting the entire market, while a change in quantity supplied/demanded involves movements along the supply or demand curve and is caused by changes in price.
Step-by-step explanation:
The difference between a change in supply/demand and a change in quantity supplied/demanded lies in their scope and cause. A change in supply or demand refers to a shift in the entire supply or demand curve, which is caused by factors such as changes in technology, input costs, or preferences. On the other hand, a change in quantity supplied or demanded refers to movement along the existing supply or demand curve due to a price change.
For example, let's say the price of smartphones increases. This would cause a decrease in the quantity demanded because consumers would be less willing to buy smartphones at a higher price. However, a change in supply/demand would occur if there was a new technology that made smartphones cheaper to produce, causing the entire demand curve to shift to the right.