Question 1

Which law states that mass is conserved in a chemical reaction, meaning the total mass of reactants equals the total mass of products?

Accepted Answer

Law of Conservation of Mass

Question 2

Given the balanced chemical equation $$2H_2 + O_2$ \rightarrow 2H_2O$$, what is the significance of the coefficients in this reaction?

Accepted Answer

They represent the relative number of moles of each substance that react or are produced.

Question 3

Which type of chemical reaction is represented by the equation $$A + B \rightarrow AB$$?

Accepted Answer

Combination/Synthesis

Question 4

A student mixes baking soda ($$NaHCO_3) $$and vinegar ($$CH_3COOH) in a $$closed container. The mass of the container and contents before and after the reaction is unchanged. Which principle does this observation best illustrate?

Accepted Answer

Law of Conservation of Mass

Question 5

Which of the following reactions is endothermic?

Accepted Answer

Photosynthesis: $$6CO_2 + 6H_2O + energy \rightarrow C_6H_{12}O_6$ + 6O_2$$

Question 6

If 4.00 g of $$NaHCO_3$$ reacts completely with excess $$CH_3COOH$$, how many moles of $$CO_2$$ are produced? ($$M_{$$NaHCO_3$$} = 84.0 \ g/mol)$$

Accepted Answer

$$0.048 \ mol$$

Question 7

Which diagram best represents the energy change in an endothermic reaction?

Accepted Answer

Reactants start lower than products; energy is absorbed.

Question 8

A nail is placed in a solution and rust forms. Which type of chemical reaction is this?

Accepted Answer

Combination/Synthesis

Question 9

Which of the following is NOT a correct use of coefficients in a balanced chemical equation?

Accepted Answer

To represent the mass of each substance.

Question 10

In a lab, a student calculates the percent yield of $$CO_2$$ from the reaction of baking soda and vinegar. If the theoretical yield is $$2.0 \ g$$ and the actual yield is $$1.6 \ g$$, what is the percent yield?

Accepted Answer

$$80\%$$

Question 11

Which statement best describes an endothermic reaction?

Accepted Answer

It absorbs heat from the surroundings.

Question 12

A student is asked to balance the equation: $$Fe + O_2$ \rightarrow Fe_2O_3. $$What are the correct coefficients?

Accepted Answer

$$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$

Question 13

Which of the following is a combination/synthesis reaction?

Accepted Answer

$$2H_2 + O_2$ \rightarrow 2H_2O$$

Question 14

During an experiment, a student observes that the temperature of the surroundings decreases as the reaction proceeds. What type of reaction is most likely occurring?

Accepted Answer

Endothermic

Question 15

Which of the following best explains why chemical equations must be balanced?

Accepted Answer

To obey the law of conservation of mass.

Question 16

A student uses a pie chart to represent the proportion of reactants and products in a chemical reaction. What does the chart illustrate?

Accepted Answer

The mass of each element before and after the reaction is equal.

Question 17

Which of the following is a correct statement about the outcome of a chemical reaction in a closed system?

Accepted Answer

The total mass of the system remains constant.

Question 18

In the reaction $$2NaHCO_3 \rightarrow Na_2CO_3 + CO_2$ + H_2O$$, how many grams of $$CO_2$$ are produced from $$16.8 \ g of$$ $$NaHCO_3$$? ($$M_{$$NaHCO_3$$} = 84.0 \ g/mol$$, $$M_{CO_2$} = 44.0 \ g/mol)$$

Accepted Answer

$$4.4 \ g$$

Question 19

Which of the following is NOT a characteristic of an endothermic reaction?

Accepted Answer

Temperature of surroundings increases

Chemical Reactions and Stoichiometry: Study Notes

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