CSI: Heat Li Keyi Danny 3S4 (15) Thermal Physics M4 Term 1
Introduction to Mystery • Fundamental Idea of Science: • Materials expand when thermal energy is applied and contracts when thermal energy is lost, due to the molecules moving more vigorously and hence maintaining a great separation.
However… • There is a certain substance that does not follow this rule, that is to say, expands when thermal energy is lost and contracts when thermal energy is gained. ??? Hmm…
Clue #1 • A bottle sealed with a heavy paper cap contains warm milk. • It is supposed to be brought into the house after the milkman place in on the doorsteps. • However, on one cold winter morning, when someone forgot to bring the milk in, the bottle was opened and milk is all on the ground! • Shows that milk expands when it freezes.
Clue #2 • A bottle containing ice frozen till the tip of the bottle is left in the sun. • When the ice had completely melted, the water level was lower than the level of the ice! • Shows that ice decreases in volume when it melts.
The Answer • Is water! • Water is made of Hydrogen and Oxygen atoms, and freezes at 0 degree Celsius. • It is also a polar molecule due to the unsymmetrical shape of the molecule and the high electro-negativity difference of hydrogen and oxygen atoms • Hence, this means that H2O molecules form hydrogen bonds among each molecules.
The Answer • When water loses thermal energy, it contracts, until it reaches a temperature of 4 degree Celsius, where it will expand instead of contracting. • This is due to the water molecules moving away from one another to rearrange themselves so that the effects of hydrogen bonding can be maximized in the structure of an ice. H2O molecules when they are in an ice lattice structure H2O molecules with hydrogen bonds
Bibliography • http://en.wikipedia.org/wiki/Water#Chemical_and_physical_properties • http://www.cmmp.ucl.ac.uk/people/finney/iceIh.jpg • http://teams.lacoe.edu/documentation/classrooms/gary/heat/activities/mystery/Mystery.html • http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/icy_ecosystems/sci_media/water_molecule/21463-1-eng-NZ/water_molecule_full_size_landscape.jpg • http://dclips.fundraw.com/zobo500dir/ice_cube_jarno_vasamaa_.jpg • http://www.biotech.wisc.edu/Outreach/FunFoodStuff/1bottlew.gif • http://www.goalfinder.com/images/articles/water%20expands%20when%20cooled%20b.gif