Evidence of chemical reactions – Flashcards
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Two different liquids are mixed together. Which observation indicates that an exothermic chemical reaction has taken place?
answer
a rise in temperature
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Iron reacts with oxygen to form iron oxide (rust). Which best describes this statement?
answer
Iron oxide is formed by rearranging atoms.
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Which statement describes a chemical reaction?
answer
Reactants form products when atoms are rearranged.
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Given below is a list of chemical reactions.
1. Burning octane fuel
2. Forming rust in an iron pipe
3. Baking a cake
4. Cement hardening
Which sequence ranks the chemical reactions in order from fastest to slowest?
answer
1, 3, 4, 2
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Which statement describes a chemical reaction?
answer
Atoms in the reactants are rearranged to form new substances.
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When two substances are mixed together, a color change is observed. Does this mean that a chemical reaction has definitely occurred?
answer
No because some physical changes produce color changes.
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During an experiment, Mr. Lehman tells his students to be alert for signs that an endothermic reaction is happening. Which of the following scenarios would his students most likely observe?
answer
A test tube becomes cool to the touch.
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The chemical formula below shows how salt is produced.
HCl + NaOH mc004-1.jpg NaCl + H2O
Which substances are the reactants?
answer
HCl and NaOH
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Which term best describes the role of hydrogen gas in the formation of a water molecule?
answer
reactant
