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1 Name: Teacher: Pd. Date: STAAR Tutorial : Energy and Matter: Elements, Compounds, and Chemical Equations: 6.5C Differentiate between elements and compounds on the most basic level. 8.5F Recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass. Elements An element is a substance that contains only one kind of atom. An element cannot be separated into simpler substances by physical or chemical means. An element is already in its simplest form. Remember: The element gold is made of gold atoms, the element aluminum is made of aluminum atoms, etc. Examples of elements: Oxygen, Potassium, Cobalt, Hydrogen, Mercury, Lead just take a look at your Periodic Table of Elements in your Reminder Binder and you will find all the elements that have been discovered and named. All elements are arranged on the Periodic Table of Elements by their properties. Elements are represented on the Periodic Table by a 1 or 2 letter symbol. If it is a 1 letter symbol it is capitalized (S for Sulfur). If it is a 2 letter symbol the first letter is capitalized and the second letter is lowercase (He for Helium). Hint: If asked how many elements are in a chemical formula just count the capital letters. Compounds A compound is a substance that is chemically made by the joining of two or more elements. Examples of compounds would be: water (H 2 O), glucose (C 6 H 12 O 6 ), carbon dioxide (CO 2 ), caffeine (C 8 H 10 N 4 O 2 )

2 Practice Problems: Write E for Element or C for Compound for each example (#1-5): 1. Fe 2 O 3 2. SiO 2 3. Zr 4. Fr 5. NaCl 6. Write an example of an element using symbol(s): 7. Write an example of a compound using symbol(s): 8. How many elements are in Asbestos H 4 Mg 3 Si 2 O 9 : and name the elements: 9. Zn + 2 HCl ZnCl 2 + H 2 : How many elements are in the reaction to left (hint: only list how many different symbols you see)? Name the elements: Chemical Equations A chemical equation describes what happens in a chemical reaction using element symbols, subscript numbers, coefficients, plus signs, and an arrow. Example of a chemical equation: Element Symbol Reaction New Substance Coefficient 2H 2 + O 2 2H 2 O Subscript: how many atoms of that element Hydrogen gas (H 2 ) can react (burn) with oxygen gas (O 2 ) to form water (H 2 0). The chemical equation for this reaction is written above. A chemical equation identifies the reactants (starting materials) and products (resulting substance), the formulas of the participants, and the amount of each substance.

3 Law of Conservation of Mass States that mass is neither created nor destroyed in any ordinary chemical reaction. Or more simply, the mass of substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants). The elements on both sides of the arrow in a chemical equation will be the same, just rearranged. In chemical equations, the amount of each substance must remain equal on both sides of the arrow to reflect the law of conservation of mass. The amount of atoms per element will be equal on both sides of the arrow in a chemical equation, just rearranged. 2H 2 + O 2 2H 2 O Look at the above chemical equation. Look at the reactants (left of arrow). What elements do you see? Hydrogen and Oxygen. What elements do you see for the product? Hydrogen and Oxygen=they are just combined (chemically). Now look at the number of each element (in the above equation). The subscript number tells you how many atoms of each element, but if you have a coefficient in front of the symbol you will have to multiply the subscript number(s) by the coefficient. 2H 2 = 4 atoms of Hydrogen (2 x 2 = 4) The coefficient only affects the element(s) in the formula it is in front of: looking at the reactants (left of the arrow) the coefficient of 2 in front of H 2 does not affect the number of Oxygen O 2. But on the product side the coefficient of 2 DOES affect Hydrogen and Oxygen. To check if the equation is balanced you must count how many atoms for each element on both sides of the arrow (reaction): 2H 2 + O 2 2H 2 O H=4 H=4 O=2 O=2 The plus sign works the same as it does in math, add atoms together for like elements. For example: 4NH 3 + 5O 2 4NO + 6 H 2 O N=4 N=4 H=12 H=12 O=10 O=10 (4+6=10)

4 Practice Problems: S 8 + 8O 2 8SO 2 1. In the above equation, how many elements combine to form the product? 2. In the above equation, write how many atoms for each element are on both sides of the equation: S= S= O= O= 4Fe + 3O 2 2Fe 2 O 3 3. In the above equation, write how many atoms for each element are on both sides of the equation: Fe= Fe= O= O= 4. In the above equation (right above #3), state what is happening to the iron and oxygen. For the following chemical equations, state whether they are Balanced or Not Balanced. 5. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 6. 2Na + 2Cl NaCl 7. 4Al + 2O 2 2Al 2 O 3 8. H 3 PO 4 + 5HCl PCl 5 + 4H 2 O 9. 2H 2 + O 2 2H 2 O How many atoms of Hydrogen were combined to form water in the equation?

5 Name: Teacher: Pd. Date: Elements, Compounds, and Chemical Equations STAAR Tutorial Quiz Answer the following questions with the best answer. You can use your Periodic Table for help. Model of Methane Molecule Hydrogen Oxygen 1. The methane molecule shown above contains how many elements? C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 2. During cell respiration, sugar (C 6 H 12 O 6 ) reacts to form carbon dioxide (CO 2 ) and water (H 2 O). Which of the following best explains what happens during cell respiration? A. A molecule is broken down into its pure elements. B. Two elements are formed into one compound. C. Single atoms are formed into different elements. D. Atoms are rearranged into different compounds. CH 4 + 2O 2 CO 2 + 2H 2 O 3. In the above equation, how many elements combine to form the products? 4. In the above equation, how many atoms of Hydrogen were combined to form water in the equation?

6 For the following chemical equations, state whether they are Balanced or Not Balanced. 5. CH 4 + 2O 2 CO 2 + 2H 2 O 6. 2NaCl + BeF 2 2NaF + BeCl Mg + Mn 2 O 3 MgO + 2Mn NH 3 + HCl NH 4 Cl 8. Why are the numbers of atoms for each element the same for the reactants and the products (why do equations have to be balanced)? State whether an element or a compound is listed below. 9. sodium= 10. vinegar=

7 Name: ANSWER KEY Teacher: Pd. Date: Elements, Compounds, and Chemical Equations STAAR Tutorial Quiz Answer the following questions with the best answer. You can use your Periodic Table for help. Model of Methane Molecule Hydrogen Oxygen 1. The methane molecule shown above contains how many elements? 2 C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 2. During cell respiration, sugar (C 6 H 12 O 6 ) reacts to form carbon dioxide (CO 2 ) and water (H 2 O). Which of the following best explains what happens during cell respiration? A. A molecule is broken down into its pure elements. B. Two elements are formed into one compound. C. Single atoms are formed into different elements. D. Atoms are rearranged into different compounds. CH 4 + 2O 2 CO 2 + 2H 2 O 3. In the above equation, how many elements combine to form the products? 3 4. In the above equation, how many atoms of Hydrogen were combined to form water in the equation? 4

8 For the following chemical equations, state whether they are Balanced or Not Balanced. 5. CH 4 + 2O 2 CO 2 + 2H 2 O Balanced 6. 2NaCl + BeF 2 2NaF + BeCl 2 Balanced 7. 3Mg + Mn 2 O 3 MgO + 2Mn UNBalanced NH 3 + HCl NH 4 Cl 8. Why are the numbers of atoms for each element the same for the reactants and the products (why do equations have to be balanced)? Due to the Law of Conservation of Mass: matter is not created nor destroyed State whether an element or a compound is listed below. 9. sodium= element 10. vinegar= compound

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