Answer:
The journal entry is as follows:
Step-by-step explanation:
January 5  Patent A/c..................Dr $100,000
 To Cash A/c............Cr $100,000
As patent is purchased so asset is increasing and any increase in asset would be debited. Therefore, patent account is debited. And it is purchased against cash and decrease in asset is credited. Therefore, cash account is credited.
December 31  Amortization expense- Patent................Dr $5,000
 To Accumulated Amortization- Patent........Cr $5,000
Working Note:
Patent Cost is $100,000
Useful life is 20 years
Amortization expense = Patent Cost / Useful life of asset
 = $100,000 / 20
 = $5,000