Horizon International School
C C
hemistry
ompetition
Answer key
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Answer
Question
Answer
Name:_________________Grade 8
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Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Which of the following is PROOF that a chemical reaction has taken place?
a. a solid forms in a liquid
b. the color of a liquid changes
c. a new substance with different properties is formed
d. a substance becomes noticeably warmer
____
2. Which of the following chemical equations is balanced?
a. 3Ca + O2  3CaO2
c. Ca + 2O2  2CaO2
b. 3Ca + 2O2  5CaO2
d. Ca + O2  CaO2
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3. Which of the following is an example of a chemical reaction?
a. ice melting in a glass of water
b. paper turning soft when wet
c. salt crystals forming as sea water evaporates
d. leaves changing colors in the fall
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4. How many carbon atoms are in this glucose molecule? C6H12O6
a. three
c. twelve
b. six
d. twenty-four
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5. Which of the following names a covalent compound?
a. aluminum sulfate
c. iron oxide
b. dinitrogen dioxide
d. sodium chloride
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6. How many sodium atoms are present in this molecule? 7Na3PO4
a. 3
c. 21
b. 7
d. 28
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7. Which of the following is an example of chemical bonds breaking?
a. an explosive breaks rocks in a mine
b. a person breaks rocks with a hammer
c. boiling water gives off steam
d. low temperatures cause icicles to form
____
8. Which of the following is NOT a sign of a chemical reaction?
a. gas formation
c. energy change
b. solid formation
d. state change
____
9. What occurs when water freezes?
a. a physical change
b. a chemical reaction
c. a chemical bond
d. a diatomic molecule
____ 10. What is the force that holds atoms together called?
a. a chemical solution
c. a chemical reaction
b. a chemical mixture
d. a chemical bond
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____ 11. A calcium carbonate molecule has 1 calcium (Ca) atom, 3 oxygen (O) atoms, and 1 carbon (C) atom. Which
of the following shows the chemical formula for calcium carbonate?
a. 3CaCO
c. CaCO3
b. Ca2 CO2
d. CaC2O3
____ 12. What is the charge of an ionic compound?
a. zero
b. 11
c. 21
d. 12
____ 13. Which is the product in this chemical formula? N + O2  NO2
a. N
c. O2
b. O
d. NO2
____ 14. Which of these uses coefficients correctly to balance this equation? N2 + H2  NH3
a. N2 + 3H2  2NH3
c. N2 + H2  NH3
b. 2N2 + 2H2  4NH3
d. 3N2 + 4H2  6NH3
____ 15. Nitrogen dioxide is a covalent compound. How many oxygen atoms are in a nitrogen dioxide molecule?
a. 3
c. 1
b. 2
d. 0
____ 16. How many oxygen atoms are present in the reactant in this chemical equation? 4Fe + 3O2  2Fe2O3
a. 2
c. 4
b. 3
d. 6
____ 17. Which chemical formula shows an endothermic reaction?
a. 4H + O2  2H2O
c. 2H2O + energy  2H2 + O2
b. 2Na + Cl2  2NaCl + energy
d. C + O2  CO2 + energy
____ 18. Which of the following is NOT an example of a chemical reaction?
a. milk turning sour
c. a match burning
b. food being digested
d. ice melting
____ 19. Which of the following is an example of a diatomic molecule?
a. NaCl
c. Mg
b. O2
d. CaCl2
____ 20. How many atoms are represented in the formula CaCO3?
a. three
c. five
b. four
d. six
____ 21. Which is the chemical formula for a dinitrogen trioxide molecule?
a. N2O3
c. 2N3O2
b. 3N2O
d. NO3
____ 22. Which example shows where a coefficient is used correctly to balance the equation?
a. Na + Cl2  2NaCl
c. 2Na + Cl2  2NaCl2
b. Na + 2Cl2  2NaCl
d. 2Na + Cl2  2NaCl
____ 23. In which kind of chemical reaction do two or more substances combine to form one new compound?
a. synthesis reaction
c. single-displacement reaction
b. decomposition reaction
d. double-displacement reaction
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____ 24. What is O2 an example of?
a. chlorophyll
b. diatomic molecule
c. chemical bond
d. sulfuric acid
____ 25. Which of the following is an example of a single-displacement reaction?
a. Fe + 2HCl  FeCl2 + H2
c. 2H2O2  2H2O + O2
b. 2Mg + O2  2MgO
d. NaOH + HCl  NaCl + H2O
____ 26. Which of the following shows an exothermic reaction?
a. 2Na + Cl2  2NaCl + energy
b. 2H2 + O2  2H2O
c. 2H2O + energy  2H2 + O2
d. 6CO2 + 6H2O + energy  C6H12O6 + 6O2
____ 27. What happens in an endothermic reaction?
a. energy is destroyed
b. energy is released
c. energy is created
d. energy is taken in
____ 28. Which of the following chemical reactions illustrates a decomposition reaction?
a. 2H2O  2H2 + O2
b. 4H2 + 2O2 2H2O
c. 6CO2 + 6H2O + energy  C6H12O6 + 6O2
d. 4KI + 2Cl2  4KCl + 2I2
____ 29. Which of the following chemical reactions illustrates a synthesis reaction?
a. 2H2O  2H2 + O2
b. 4H2 + 2O2  2H2O
c. 6CO2 + 6H2O + energy  C6H12O6 + 6O2
d. 4KI + 2Cl2  4KCl + 2I2
____ 30. Most covalent compounds
a. dissolve in water.
b. don’t dissolve in water.
c. mix with water.
d. are positively charged in water.
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