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Chemistry Q/ Definitions : 1- Law of Conservation of Mass: Matter is neither created nor destroyed. 2- Law of constant composition: The composition of elements are constant in all samples of a compound. 3- Law of Combining Gas Volumes: The volumes of gases...

Chemistry Q/ Definitions : 1- Law of Conservation of Mass: Matter is neither created nor destroyed. 2- Law of constant composition: The composition of elements are constant in all samples of a compound. 3- Law of Combining Gas Volumes: The volumes of gases involved in or resulting from the chemical reaction correspond to each other by a simple numerical proportionality if measured under the same conditions of pressure and temperature. 4- Avogadro’s Hypothesis: Equal volumes of gases contain equal number of molecules under the same pressure and temperature conditions. 5- Valence: It is the number of electrons which an element loses, gains or shares during a chemical reaction. 6- Atomic Mass: Unit:The mass of C-12 isotope is accepted as 12.0000 and 1/12 of this is called as 1 atomic mass unit (amu). 7- Equivalent mass: The mass of that element which combine with eight mass parts of oxygen or pull these quantities from their compounds. 8- Empirical Formula: It is the simplest formula that gives the minimum limit of absolute information about the compound, it sets the rational number of the atoms included in the compound. 9- Molecular Formula: It is the chemical formula that gives the real number of the atoms of elements that involve in the composition of one molecule of the matter. 10- Temperature: Degree of temperature is used to tell to express that some objects have high or low temperatures; temperature tells which way heat flows. Heat flow occure from a cold object to a hot object spontaneously. Temperature has got three units. Centigrade (C˚), Kelvin (K) and Fahrenheit (F˚). 11- Avogadro’s Number: It is either number of atoms in 1 mole of an element or number of molecules in 1 mole of a compound. Its value is 6.023×1023. 12- Molar mass: It is the unit of mass of 1 mole of atom or 1 mole of molecule in gram unit. Its unit is g/ mol. 13- Mole (n): The amount of substance which contains, molecules or ions as many as Avogadro’s number is called as 1 mole of substance. 14- Avogadro defined : Molecule as: the smallest independent sample of matter. He also define atom as: the smallest part of an element which can be found in molecules of different compounds. 15- STP : standard temperature and pressure. The conditions at which temperature is ( 0°C ) and pressure is (1 atm). Q/ Dalton s atomic theory ? An: 1- The substance consists of small, indivisible particles called "atoms" (which the scientists later managed to fragment). 2- Atoms cannot be synthesized, within the human abilities. 3- Atoms of the same element are similar in all their physical and chemical properties and differ from the atoms of other elements. 4- Compound atoms (as called by Dalton) are formed by the union of atoms of the elements atoms with simple ratios. Q/what is Avogadro s hypothesis ? Give an example about it ? An: Avogadro’s Hypothesis: Equal volumes of gases contain equal number of molecules under the same pressure and temperature conditions. For example : 1- One volume of hydrogen is combined with one volume of chlorine, and two volumes of hydrogen chloride are formed, the ratio between the two united gaseous volumes and the volume of gas produced is 1:1: 2, as in the following chemical equation: H2 + Cl2 → 2HCl. 2- When the water is electrically analyzed, the volume of the freed hydrogenis twice the volume of the oxygen, and it combines two volumes of hydrogen with one volume of oxygen and produces two volumes of water vapour. 2H2 +O2 → 2H2O The ratio between the two volumes united gaseous sizes and the volume of water vapour produced is 2:1:2, which is a simple numerical ratio. Q/ All laws : 1- Mass conservation: The mass of reactants(the summation) = the mass of products(the summation) from the reaction 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 2- Constant composition: the ratio = 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 = the ratio = 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 =  𝑎𝑡𝑜𝑚𝑖𝑐 𝑚𝑎𝑠𝑠 3- Atomic mass: Absolute mass of element = 𝑎𝑣𝑜𝑔𝑎𝑑𝑟𝑜 𝑠 𝑛𝑢𝑚𝑏𝑒𝑟 (Avogadro s number = 6.023× 1023 ) 𝑚 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 1𝑠𝑡 𝑚 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 2𝑛𝑑 4- Equivalent mass: = 𝐸𝑞.𝑚 1𝑠𝑡 𝐸𝑞.𝑚 2𝑛𝑑 5- relationship between Atomic mass , equivalent mass and valence : 𝑎𝑡𝑜𝑚𝑖𝑐 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 Eq.m element = 𝑣𝑎𝑙𝑒𝑛𝑐𝑒 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑚(𝑔) 6- Density if gases: 𝜌(𝑔/𝑐𝑚3 ) = 𝑣(𝑐𝑚3 ) 𝑚(𝑔) 7- Mole concept: A) n(mol) = 𝑔 Molar mass = (‫ عدد الذرات‬+ ‫ )الكتلة الذرية‬+ ( same ) … 𝑀(𝑚𝑜𝑙) 𝑛𝑜.(𝑎𝑡𝑜𝑚𝑠,𝑖𝑜𝑛𝑠 𝑜𝑟 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠) B) number of moles = 𝐴𝑣𝑜𝑔𝑎𝑑𝑟𝑜 𝑠 𝑛𝑢𝑚𝑏𝑒𝑟 8- Mass percentage of element in a compound: 𝑀 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 % 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑖𝑛 𝑎 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 = = 100% 𝑀 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 9- Mass of element in a compound: 𝑀 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 𝑖𝑛 𝑐𝑎 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 = × 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 𝑀 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 10- Empirical formula: 𝑚𝑎𝑠𝑠 𝑜𝑟 % 𝑜𝑓 𝑒𝑙𝑒𝑚𝑒𝑛𝑡 1- Ratio of no. of atom = 𝑎𝑡𝑜𝑚𝑖𝑐 𝑚𝑎𝑠𝑠 𝑟𝑎𝑡𝑖𝑜 𝑜𝑓 𝑎𝑡𝑜𝑚 2- Simple no. of atom = 𝑙𝑜𝑤𝑒𝑠𝑡 𝑟𝑎𝑡𝑖𝑜 11- Molecular formula: Molecular formula = empirical formula × empirical formula unit 𝑀 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 a- Empirical formula unit = 𝑀 𝑒𝑚𝑝𝑖𝑟𝑖𝑐𝑎𝑙 𝑓𝑜𝑟𝑚𝑢𝑙𝑎 Empirical formula ‫ نستخرج ال‬-1 Molar mass of empirical formula ‫ نستخرج ال‬-2 Empirical formula unit ‫ نستخرج ال‬-3 Molecular formula ‫ واخيرا نستخرج ال‬-4