Laser tissue welding is a thermal process for binding tow tissues together. Optical and thermal models exist to calculate the temperatures of laser irradiated tissues. However, a rate process model is required to relate the time-temperature history to a weld strength. This paper proposes a first-order rate process model based on contraction during heating. The entropy and enthalpy associated with contraction of porcine intestine in a water bath was measured and used to calculate the fraction of altered molecules for both water bath and laser welding. Intestine was welded to intestine in a water bath at 60-80 degrees C for seven minutes. Pulsed laser welding used 10-30 pulses and an exogenous chromophore. The yield strengths of the welds were measured and found to roughly correlate with the fraction of altered molecules estimated for both the water bath and laser welds.