Keystore Systems experienced the following accounting events during its 2012 accounting period.
1. Paid cash to purchase land.
2. Recognized revenue on account.
3. Issued common stock.
4. Paid cash to purchase supplies.
5. Collected a cash advance for services that will be provided during the coming year.
6. Paid a cash dividend to the stockholders.
7. Paid cash for an insurance policy that provides coverage during the next year.
8. Collected cash from accounts receivable.
9. Paid cash for operating expenses.
10. Paid cash to settle an account payable.

Required
a. Identify the events that would require a year-end adjusting entry.
b. Explain why adjusting entries are made at the end of the accounting period.