Why did early scientists believe that heat was a fluid

Based on the position vs. time graph which velocity vs. time graph would correspond to the data

An exothermic reaction is conducted in an insulated calorimeter filled with water. the calorimeter is then sealed so that there is no heat exchanged between the contents of the container and the surrounding air. which of the following statements is true about the reaction?

Fill in the coefficients that will balance the following reaction: a0cr2(so4)3 + a1agno3 -> a2cr(no3)3 + a3ag2so4