[Grammar] an order for/of

[Snappy]

Are "for" and "of" interchangeable in the following cases?

We had two orders of pizza.
We placed an order for a new computer.

 

[bhaisahab]

Are "for" and "of" interchangeable in the following cases?

We had two orders of pizza.
We placed an order for a new computer.

If you change "of" to "for" in the first sentence it would be a correct sentence but would have a different meaning, you could say it if, for example, you run a restaurant and last night you had two customers who ordered pizza.
The second sentence would just be incorrect.