Question 1

Which of the following is an example of a chemical change?

Accepted Answer

Burning wood in a fireplace

Question 2

According to the Law of Conservation of Mass, what must be true for any chemical reaction?

Accepted Answer

The mass of the reactants equals the mass of the products

Question 3

Which of the following is NOT evidence that a chemical reaction has occurred?

Accepted Answer

Change in shape

Question 4

A student mixes two clear solutions and observes a sudden formation of a solid. What is the name of the solid formed?

Accepted Answer

Precipitate

Question 5

Which statement best describes the collision theory?

Accepted Answer

Reacting particles must collide with enough energy to form new bonds

Question 6

Given the unbalanced equation: $$\mathrm{Cu(s) + O_2$(g) \rightarrow CuO(s)}$$, what is the correct balanced equation?

Accepted Answer

$$\mathrm{2Cu(s) + O_2$(g) \rightarrow 2CuO(s)}$$

Question 7

In the reaction $$\mathrm{2Na(s) + Cl_2$(g) \rightarrow 2NaCl(s)}$$, what is the ratio of sodium atoms to chlorine molecules?

Accepted Answer

2:1

Question 8

Which of the following best explains why coefficients are used to balance chemical equations?

Accepted Answer

Coefficients ensure the Law of Conservation of Mass is not violated

Question 9

A reaction is written as $$\mathrm{NaCl + $$AgNO_3$$ \rightarrow AgCl + $$NaNO_3$$}. $$Which substance is the reactant?

Accepted Answer

NaCl

Question 10

Which notation correctly represents an aqueous solution?

Accepted Answer

(aq)

Question 11

If a chemical equation is not balanced, which law is being violated?

Accepted Answer

Law of Conservation of Mass

Question 12

Which of the following is a physical change?

Accepted Answer

Boiling water

Question 13

In the equation $$\mathrm{2Na(s) + Cl_2$(g) \rightarrow 2NaCl(s)}$$, what does the (s) notation indicate?

Accepted Answer

The substance is a solid

Question 14

Which of the following would require balancing the equation by changing coefficients, not subscripts?

Accepted Answer

Changing $$\mathrm{2H_2 + O_2$ \rightarrow 2H_2O} to$$ $$\mathrm{4H_2 + 2O_2 \rightarrow 4H_2O}$$

Question 15

A student observes a sudden temperature increase during a reaction. What does this indicate?

Accepted Answer

A chemical reaction has occurred

Question 16

Which of the following equations is balanced?

Accepted Answer

$$\mathrm{2NaOH(aq) + $$CaBr_2$$(aq) \rightarrow Ca(OH)_2(s) + 2NaBr(aq)}$$

Question 17

Which step is NOT part of the process for balancing a chemical equation?

Accepted Answer

Change the subscripts of the compounds

Question 18

A reaction produces heat and light. What type of change is this?

Accepted Answer

Chemical change

Question 19

In the equation $$\mathrm{$$AlBr_3$$(aq) + K_2SO_4(aq) \rightarrow KBr(s) + Al_2$(SO_4$)_3(aq)}$$, which product is a solid?

Accepted Answer

KBr(s)

Question 20

If a reaction starts with 25 g of reactants, how many grams of products should be formed according to the Law of Conservation of Mass?

Accepted Answer

25 g

Chemical Reactions and Balancing Equations: Study Notes

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