Is there a difference between the accounts Purchases and Inventory?

Yes, there is a difference between purchase and inventory accounts:-

All purchases done in a period (say quarterly, half-yearly / yearly) will be recorded individually in the purchase account from various purchasers and will be transferred to inventory at the end of the period. 

In other words - Inventory = Purchase for the period + old purchase (combine together)

No difference between purchase and inventory account

Accouts is a art of Classicfing Summarising Ina sytematical Maneer

Purchase Is The Thing Wat We are Going TO purchase And It Will Be Recorded In records  oF accounts

And The Recorded &Purchase Materail Will Be Kept In store Is Call Inventary

The account Purchases is generally associated with the purchase of inventory items under the periodic inventory system. ... The cost of the ending inventory is computed through a physical count (or an estimate) and is subtracted from the cost of goods available. The resulting amount is the cost of goods sold.

 you  can say  the purchase ,as reflect mirror of the inventory