> An expense account is an account that records expenses incurred such as your AWS bill, rent payments or salaries paid.
Ah.
> These are not liabilities
Well, that depends.
Every expense that involves an invoice or purchase order that is not paid immediately in cash must be recorded as two transactions. The first transaction is the issuing of the invoice or the PO. That transaction is a liability to the buyer, an asset to the seller. The second transaction is the payment of the invoice. That transaction involves a decrease in the buyer's cash reserves (asset) and a discharge (decrease) of the the buyer's liability, and an increase in the seller's cash reserves (asset) and a decrease in the seller's accounts receivable (asset).
When I look in "accounting for dummies" type web sites, they all give examples of expense accounting as a single transaction. That is deeply broken. If you try to record an expense as a single transaction then your balance sheet is going to be wrong if you have any unpaid invoices, either payable or receivable. In fact, recording an expense as a single transaction doesn't even work if you're paying cash in a brick-and-mortar store unless you literally keep all your cash as physical cash in a safe because ATM withdrawals are transactions that need to be recorded too.
In a situation like an employee being reimbursed for a travel expense there are at least four transactions:
1. The employee using their credit card to buy something (liability to the employee, asset to the merchant)
2. The merchant getting paid by the credit card company (converting a receivable into cash, i.e. trading one asset type for another)
3. The employee submitting their expense report (invoice) to the company for reimbursement (liability to the company, asset to the employee)
4. The employee getting paid by the company for the incurred expense (company converts asset into a discharge of liability, employee converting receivable into cash)
I say "at least" because if there is a credit card involved then step 2 actually involves a bank issuing a loan to the credit card holder, so there is an additional entity involved, and more transactions on their end. And of course when I say "cash" I actually mean "demand deposit" which is not quite the same thing, though people tend to conflate the two.