1 litre tank water sealed does steam pressure rise linear or exponential?

hi, if you had a litre container full of water with negligible air and nothing else and heated it at a linear rate from 50 degrees centigrade upto 200 degrees centigrade does the steam pressure rise linearly or exponentially?
the measurements are plucked from the air, its the rate of steam pressure increase above 100 deg c in a sealed tank im interested in.

i failed science at school and need this confirmed before i build something. thanks
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 Is the heat input linear, energy added per time, or the temperature rise, degrees centigrade change per time?
 Worst case estimate, consider the water to be an ideal gas. Adding energy to an ideal gas in a closed, thermally insulated container one can just use the ideal gas law to find the pressure?