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40558_Ward's World+MGH Water

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1 Water Article by: Harold L. Friedman. Department of Chemistry, State University of New York, Stony Brook, New York. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource that provides immediate, authoritative answers to students' thirst for scientific knowledge on topics such as climate change, virology, pollution, and more. Ward's World and McGraw Hill have partnered to offer educators a no-obligation, free trial subscription to this product. Request your free trial today and discover how valuable AccessScience can be for you and your students. A clear, odorless, tasteless liquid at 0 to 100°C, formula H2O, also known as dihydrogen oxide. Water also exists in the vapor (gaseous) and solid (ice) states under normal terrestrial conditions and is a solvent for many substances (Fig. 1). Water is essential for life and is the most abundant molecule on Earth. Water vapor is a green- house gas. On Earth, water vapor and carbon dioxide provide most of the greenhouse warming to maintain a global mean surface temperature of about 15°C, allowing for liquid water. Formation It is formed by the direct reaction (1) of hydrogen with oxygen. 2H2 + O2 —> 2H2O The other compound of hydrogen and oxygen, hydrogen peroxide, readily decom- poses to form water, reaction (2). 2H2 + O2 —> 2H2O + O2 Water also is formed in the combustion of hydrogen-containing compounds, in the pyrolysis of hydrates, and in animal metabolism. Some properties of water are given in the table. + ward ' s science Content • Formation • Gaseous state • Solid state • Liquid state • Solutions in water • Chemical properties Key Concepts • Water (chemical formula H2O) is the most abundant molecule on Earth. • Water can occur as a solid (ice), a liquid, or a gas (water vapor), depending on environmental temperature and pressure. • The net attraction that holds water molecules together is called hydrogen bonding. • The unusual strength of hydrogen bonds results in water's many unique properties, such as ice's low density and buoyancy, and liquid water's extremely high boiling point, high heat of vaporization, and high electrical conductivity. • Water is an excellent solvent for many substances but is not a strong oxidizing or reducing agent. • Strong acids and bases react with water. Fig. 1: Molecular model of water. Hydrogen is shown in white and oxygen is shown in red.

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