Expected score in my first FIDE tournament Going to play my first international tournament next week.

As this is my first I do not have a FIDE ELO (I have national rating however). 

How will my games be rated and how is my expected score for each game calculated?
The FIDE Rating Regulations give details of how the system works. You should scroll down to section 8. The working of the FIDE Rating System
which describes the mathematical tables and formulae used for calculating ratings.

Note that a fudge factor called the "Development Coefficient" is used in calculating ratings which determines by how much new results affect your existing rating once you have one. 


  K = 40 for a player new to the rating list until he has completed
  events with at least 30 games
  
  K = 20 as long as a player's rating remains under 2400.
  
  K = 10 once a player's published rating has reached 2400 and remains
  at that level subsequently, even if the rating drops below 2400.
  
  K = 40 for all players until their 18th birthday, as long as their
  rating remains under 2300.


As a new player you will have a high K which will mean that your rating will change rapidly if you have results which vary widely from your previous results.