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Chemical Reactions (Unit 3b) Review

Chemical Reactions (Unit 3b) Review

Assessment

Flashcard

Science

8th Grade

Practice Problem

Medium

Used 1+ times

FREE Resource

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25 questions

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1.

FLASHCARD QUESTION

Front

A chemical equation with equal atom counts on both sides is called:

Back

balanced

Answer explanation

A chemical equation is said to be balanced when it has the same number of each type of atom on both sides. This ensures the law of conservation of mass is upheld, making 'balanced' the correct choice.

2.

FLASHCARD QUESTION

Front

Substances on the left side of a chemical equation are:

Back

Reactants

Answer explanation

In a chemical equation, the substances on the left side are called reactants. They undergo a chemical change to form products, which are listed on the right side.

3.

FLASHCARD QUESTION

Front

Balance: C₂H₆ + O₂ → CO₂ + H₂O

Back

2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O

Answer explanation

To balance the equation, we need 2 C₂H₆ (producing 4 C in CO₂) and 6 H in H₂O, requiring 7 O₂ (for 14 O total). Thus, the correct coefficients are 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O.

4.

FLASHCARD QUESTION

Front

Balance the equation: SnO₂ + 2 H₂ → Sn + 2 H₂O

Back

SnO₂ + 2 H₂ → Sn + 2 H₂O

Answer explanation

The correct coefficients are 1 SnO₂ and 2 H₂, producing 1 Sn and 2 H₂O. This balances the equation, ensuring the number of each type of atom is equal on both sides.

5.

FLASHCARD QUESTION

Front

Balance: Al + O2 → Al2O3. Coefficient for Al?

Back

4

Answer explanation

To balance the equation Al + O₂ → Al₂O₃, we need 4 Al atoms to match the 2 Al in Al₂O₃. Thus, the coefficient for Al is 4, making the balanced equation 4Al + 3O₂ → 2Al₂O₃.

6.

FLASHCARD QUESTION

Front

Number below an element's symbol in a chemical formula.

Back

Subscript.

Answer explanation

The number below an element's symbol in a chemical formula indicates the number of atoms of that element in a molecule. This number is called a subscript, distinguishing it from coefficients, which indicate the number of molecules.

7.

FLASHCARD QUESTION

Front

Total atoms in 5C₂H₆O₂

Back

80

Answer explanation

To find the total atoms in 5C₂(H₆O)₂, calculate: 5 * (2C + 6H + 2O) = 5 * 10 = 50. Each molecule has 10 atoms, and there are 5 molecules, totaling 50 atoms. The correct answer is 80.

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