Chemical Reactions
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A chemical reaction involves the transformation of reactants into different products through rearrangement of atoms. Chemical reactions conserve mass as atoms are not destroyed or created, but instead are reorganized into new substances. Balancing chemical equations ensures the same number and type of atoms are on both sides of the reaction.
Chemical Reactions
- 2. CHEMICAL REACTIONS a chemical change is the transformation of one or more substances into new substances with new properties
- 3. A chemical reaction is the process by which a chemical change happens. All chemical reactions are also accompanied by changes in energy CHEMICAL REACTIONS
- 4. Some chemical reactions absorb energy, such as in the chemical reactions that cook food. CHEMICAL REACTIONS
- 5. CHEMICAL REACTIONS Other chemical reactions release energy in the form of heat , light and/or sound , such as the burning of wood in a campfire
- 6. CHEMICAL REACTIONS Chemical reactions happen at different rates . Some chemical reactions are fast , such as when rocket fuel burns.
- 7. Other chemical reactions happen slowly , such as the formation of rust on a corroding bicycle chain.
- 8. The chemical reactions in your own body , which are keeping you alive, are among the fastest chemical reactions known. CHEMICAL REACTIONS
- 9. Chemical reactions are used in many ways in daily life. CHEMICAL REACTIONS
- 10. Scientists are constantly working to find new kinds of chemical reactions in order to produce new substances with useful properties .
- 11. All chemical reactions involve the conversion of starting materials, called reactants , into new substances, called products . REACTANTS & PRODUCTS
- 12. The products have different properties than the reactants. These new reactions may produce substances with different colours or states (solid, liquid, gas) REACTANTS & PRODUCTS
- 13. For example, when a piece of solid magnesium metal is placed into a solution of hydrochloric acid, bubbles of hydrogen are formed as well as aqueous magnesium chloride REACTANTS & PRODUCTS
- 14. A chemical reaction is often described by writing a chemical equation CHEMICAL EQUATIONS
- 15. A chemical equation uses either words or symbols and formulas to describe the changes that occur during a chemical reaction . CHEMICAL EQUATIONS
- 16. For example, the chemical reaction between solid magnesium metal and hydrochloric acid is: CHEMICAL EQUATIONS word equation: magnesium + hydrochloric acid magnesium chloride + hydrogen formula equation: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g)
- 17. Notice that hydrogen is expressed in the formula equation as H 2 . Recall that pure hydrogen exists as a diatomic molecule . (You will need to know which elements exist as molecules when writing formula equations) CHEMICAL EQUATIONS word equation: magnesium + hydrochloric acid magnesium chloride + hydrogen formula equation: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g)
- 18. The chemical formulas in a formula equation will often include the following: the state of matter of each substance (s) = solid (l) = liquid (g) = gas (aq) = aqueous CHEMICAL EQUATIONS
- 19. The chemical formulas in a formula equation will often include one or more coefficients A coefficient is an integer that is placed in front of the symbol of an element to show the ratios of the different substances that are present in the chemical reaction CHEMICAL EQUATIONS
- 20. For example, in the formula equation above, a coefficient of 2 is in front of the formula HCl . This means that Mg and HCl combine in a ration of 1:2 CHEMICAL EQUATIONS formula equation: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g)
- 21. The total mass of reactants and the total mass of products in a reaction are always the same . In other words, the mass is conserved CONSERVATION OF MASS
- 22. In a chemical reaction, the mass of the products always equals the mass of the reactants. Law of Conservation of Mass:
- 23. No atoms are destroyed and no new atoms are produced during a chemical reaction. Instead, the atoms in the reactants are simply rearranged to form the products Chemical bonds between atoms are broken and new ones are formed , and the atom simply reconnect in new ways CONSERVATION OF MASS
- 24. The rearrangement of atoms that occurs during a chemical reaction can be illustrated using models or diagrams. For example : word equation : hydrogen + oxygen water formula equation : 2H 2 (g) + O 2 (g) 2H 2 O(l) REACTANTS & PRODUCTS
- 25. In this equation, there are equal numbers of hydrogen atoms ( 4 ) and equal numbers of oxygen atoms ( 2 ) on both the reactants side and the products side. formula equation : 2H 2 (g) + O 2 (g) 2H 2 O(l) REACTANTS & PRODUCTS
- 26. When the number of each kind of atom is the same in the reactants and products, the equation is said to be balanced . formula equation : 2H 2 (g) + O 2 (g) 2H 2 O(l) REACTANTS & PRODUCTS
- 28. A chemical reaction that is complete except for coefficients is called an unbalanced equation or skeleton equation. BALANCING CHEMICAL REACTIONS
- 29. To balance a chemical equation, begin by counting the number of atoms of each element in the skeleton equation. BALANCING CHEMICAL REACTIONS
- 30. Balance by placing coefficients in front of the chemical formulas . Never change a subscript in a formula to help make atoms balance! BALANCING CHEMICAL REACTIONS
- 31. Balance atoms of elements in any complicated looking formulas first and balance atoms of pure elements last. BALANCING CHEMICAL REACTIONS H 2
- 32. Hydrogen atoms and/or oxygen atoms will often appear in many or all of the formulas of the reactants and products. When this is the case, balance other elements first, balance hydrogen second last and oxygen last . BALANCING CHEMICAL REACTIONS
- 33. You may be able to treat polyatomic ions as a unit . ex.) if NO 3- appears in the reactants and products of a skeleton equation, count the number of NO 3- groups rather than the number of N and O atoms separately. BALANCING CHEMICAL REACTIONS
- 34. Example 1: Balance the following chemical equation: AlBr 3 (s) + Cl 2 (g) AlCl 3 (s) + Br 2 (g) 1.) Count the number of atoms in the reactants and products: BALANCING CHEMICAL REACTIONS
- 35. Example 1: 2 AlBr 3 (s) + Cl 2 (g) AlCl 3 (s) + 3 Br 2 (g) Balance the number of bromine atoms by adding a coefficient of 2 in front of AlBr 3 and a coefficient of 3 in front of Br 2 . Count the atoms again: BALANCING CHEMICAL REACTIONS
- 36. Example 1: 2 AlBr 3 (s) + Cl 2 (g) AlCl 3 (s) + 3 Br 2 (g) The number of aluminum atoms is no longer equal. BALANCING CHEMICAL REACTIONS
- 37. Example 1: 2 AlBr 3 (s) + Cl 2 (g) 2 AlCl 3 (s) + 3 Br 2 (g) Balance the number of aluminum atoms by adding a coefficient of 2 in front of AlCl 3 . Count the atoms again: BALANCING CHEMICAL REACTIONS
- 38. Example 1: 2 AlBr 3 (s) + Cl 2 (g) 2 AlCl 3 (s) + 3 Br 2 (g) The number of chlorine atoms is no longer balanced. BALANCING CHEMICAL REACTIONS
- 39. Example 1: 2 AlBr 3 (s) + 3 Cl 2 (g) 2 AlCl 3 (s) + 3 Br 2 (g) Balance the number of chlorine atoms by adding a coefficient of 3 in front of Cl 2 . Count the atoms again: BALANCING CHEMICAL REACTIONS
- 40. Example 1: 2 AlBr 3 (s) + 3 Cl 2 (g) 2 AlCl 3 (s) + 3 Br 2 (g) The equation is balanced! BALANCING CHEMICAL REACTIONS
- 41. Try it! Balance the following chemical equations: Al + F 2 AlF 3 Ca + H 2 O Ca(OH) 2 + H 2 CaCl 2 + Na 3 PO 4 Ca 3 (PO 4 ) 2 + NaCl BALANCING CHEMICAL REACTIONS
- 42. Try it! Balance the following chemical equations: 2 Al + 3 F 2 2 AlF 3 Ca + 2 H 2 O Ca(OH) 2 + H 2 3 CaCl 2 + 2 Na 3 PO 4 Ca 3 (PO 4 ) 2 + 6 NaCl BALANCING CHEMICAL REACTIONS