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c0203

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  • 1. Chemistry Item 02-03 Which set of coefficients correctly balances the equation KClO 3  KCl + O 2 ?   A. 111 B. 123 C. 223 D. 323 www.upcatreview.com
  • 2. Chemistry Item 02-03 CONCEPT : A chemical equation shows the kind and amount of substances that took place in a chemical reaction represented by symbols and formulas. For chemical equations to represent a chemical reaction correctly, it is important to write the correct formula for the reactants and the products and then balanced to be consistent with the law of conservation of mass. www.upcatreview.com
  • 3. Chemistry Item 02-03 To balance the equation would mean that each side of the equation has equal number of atoms of each element. When balancing equations, it is important to note that the identity of the atoms must not be changed thus the subscripts of the chemical formula must never be changed nor can atoms be added or subtracted from a formula. Some important reminders when balancing an equation are as follows: www.upcatreview.com
  • 4. Chemistry Item 02-03
    • Balancing an equation is done by inspection, starting with the most complicated molecules one element at a time.
    www.upcatreview.com
  • 5. Chemistry Item 02-03
    • Any addition to the number of atoms of a particular element is done by writing coefficients , which is a small whole number placed in front of a chemical formula in the equation. A chemical formula without any written coefficient is understood to have a coefficient of 1.
    www.upcatreview.com
  • 6. Chemistry Item 02-03
    • Coefficients to be used should be in the lowest possible ratio.
    www.upcatreview.com
  • 7. Chemistry Item 02-03 Balancing the reaction given in the previous problem,   KClO 3  KCl + O 2 www.upcatreview.com
  • 8. Chemistry Item 02-03 The most complicated molecule is KClO 3 . Balancing can begin by inspecting the product that contains the atoms in KClO 3 . The no. of atoms for both K and Cl are already equal except for oxygen. The left side has three atoms of oxygen while only 2 on the right side. www.upcatreview.com
  • 9. Chemistry Item 02-03 Usually, this set of coefficients is balanced by writing a coefficient of 3 before the oxygen on the right side then a coefficient of 2 is placed before KClO 3 making the number of oxygen atoms 6 for both sides. www.upcatreview.com
  • 10. Chemistry Item 02-03 2 KClO 3  KCl + 3 O 2 (6 O atoms) (6 O atoms) (2 K atoms) (1 K atoms) (6 Cl atoms) (1 Cl atoms) www.upcatreview.com
  • 11. Chemistry Item 02-03 And since the balancing of oxygen atom affected the number of K and Cl atoms on the left side, a coefficient of 2 is added before KCl on the right to balance the equation. www.upcatreview.com
  • 12. Chemistry Item 02-03 Now check the equation: 2 KClO 3  2 KCl + 3 O 2 (6 O atoms) (6 O atoms) (2 K atoms) (2 K atoms) (2 Cl atoms) (2 Cl atoms) www.upcatreview.com
  • 13. Chemistry Item 02-03 Thus the final answer would be 2 KClO 3  2 KCl + 3 O 2 ( equation is balanced ). The summary of coefficients is 2 2 3 ( letter C ). www.upcatreview.com