The chemical reaction for CFC is: CCl3F = CCl2F + Cl. Uses. Due to their chemical properties, CFCs became useful as coolants and propellants. More commonly known as freon for refrigeration, CFCs are used extensively in appliances as a safe method of refrigeration. The other main use for CFCs has been as a propellant for aerosol cans.
The earliest known Egyptian pyramids are found at Saqqara, northwest of Memphis. The earliest among these is the Pyramid of Djoser (constructed 2630 BCâ2611 BC) which was built during the third dynasty. This pyramid and its surrounding complex were designed by the architect Imhotep, and are generally considered to be the world's oldest monumental structures constructed of dressed masonry.
All three of Giza's famed pyramids and their elaborate burial complexes were built during a frenetic period of construction, from roughly 2550 to 2490 B.C. The pyramids were built by Pharaohs Khufu (tallest), Khafre (background), and Menkaure (front).is Great Pyramid is the largest in Giza and towers some 481 feet (147 meters) above the plateau. Its estimated 2.3 million stone blocks each weigh an average of 2.5 to 15 tons. Khufu's son, Pharaoh Khafre, built the second pyramid at Giza, circa 2520 B.C.