I copied your code and organized it a bit:
bedroom is a room.
The padlock is in the bedroom.
The padlock is a container.
The padlock is locked.
The description is "A solid padlock with a small key hole."
Every turn when padlock is locked and the chain is examined:
say "You are locked to a bed by a chain and can't move far.";
output:
Welcome
An Interactive Fiction
Release 1 / Serial number 250402 / Inform 7 v10.1.2 / D
bedroom
You can see a padlock (closed) here.
>z
Time passes.
You are locked to a bed by a chain and can’t move far.
So far as mentioning or not mentioning the padlock, depending on whether or not the chain has been examined, there are a few options. Perhaps the padlock is attached to the chain:
the padlock is part of the steel chain
You can conceal it until the player examines it:
rule for deciding the concealed possessions of the steel chain:
if we have examined the steel chain:
decide no;
otherwise:
decide yes.
In this case, the padlock is a “possession” of the steel chain because it is part of it. The posessions of the chain are concealed until the player examines the chain. This can be tied into your every turn rule:
Every turn when padlock is locked and the padlock is not concealed:
say "You are locked to a bed by a chain and can't move far.";
output:
>z
Time passes.
>z
Time passes.
>x chain
You see nothing special about the steel chain.
You are locked to a bed by a chain and can’t move far.
>z
Time passes.
You are locked to a bed by a chain and can’t move far.
Another option is just moving it:
After examining the steel chain:
now the padlock is in the bedroom;
(You could make it scenery, or make it part of scenery, but I’m assuming you don’t want players to interact with it before it’s discovered)