The difference between a change in quantity supplied and a change in supply is that a change in quantity supplied is a shift along the supply curve, while a change in supply is a shift of the entire supply curve.

In the demand and supply graph, supply slopes upwards, so that as price increases supply increases. This makes logical sense as suppliers want to sell more products if the price is higher. A change in quantity supplied can happen for a number of reasons. If there is an increase in demand, and the intersection between the two is moved, then there is a shift in quantity supplied. If there is a tax or tariff implemented, this would cause market limitations and another shift along the supply curve to meet the new strains of the market.

Changes in supply are caused by external factors that move the quantity supplied at every single price point. It is not just a move along the curve but an entire shift. For example, if we're looking at the demand and supply graph for corn, when there is a drought and crops aren't performing well, there would be a change in supply entirely as the supply curve shifts to the left due to less product being available.