The diagram shows a heating curve for a substance. a graph titled heating curve of substance it shows heat added in joules on the x-axis, and temperature in degrees celsius on the y-axis on a scale of 0 to 100. the graph has a diagonal line from negative 5 degrees up to zero degrees labeled u. a horizontal line segment at zero degrees labeled v. a diagonal line segment from zero degrees up to 120 degrees labeled w. a horizontal line segment at 120 degrees labeled x and then another diagonal segment labeled y. which segment shows the substance changing from a gas to a liquid? x-y y-x w-x x-w