Iowa is not a community property state. The debts of the deceased spouse do not become the debts of the surviving spouse (unless they were joint debts). The estate is responsible for payment. As a practical matter, to the extent that some estate assets may be required to be sold to satisfy such debts, a surviving spouse may be affected.
Note: In some jurisdictions, the "law of necessaries" is followed. Basically, this requires a surviving spouse to repay debts of a deceased spouse if they were incurred for the benefit of the family. However, only those such debts would have to be paid. Additionally, many places do not adhere to this doctrine.
You should consult with an attorney in your area as to your specific state law.