We were working with matter and different temperatures.  We were testing at what temperature the solid chocolate would start to change to a liquid.  We found the lower temperatures did not cause a change in the solid.  But the higher temperature did cause a change in the solid.  The temperature that caused the change was around 40 degrees Celsius. 
"The hot water in the cup made the chocolate chip melt." Jacob
"The cold water did not change the chocolate chip at all because heat is needed to change the chocolate chip." Emma
"Heat can cause changes in some solids." Artan