If / When

Two sentences - "If  you clean your room, you can have a treat."  "When you clean your room, you can have a treat."  Is there a difference between those statements?  There most certainly is!  The first one implies doubt and uncertainty.  There is an unspoken opinion that you don't think the job will get done.  The second sends a positive message.  It clearly implies the expectation that the job will get done.  Which message do you want to send to your child?  Surprisingly, the negative approach seems to be much more commonly used.  Too bad...When you speak positively to your children, they will be more inclined to to what they are asked.