Describing Chemical Reactions

Which of the following statements is true about what happens in all chemical reactions?

• The ways in which atoms are joined together is not changed.

• New atoms are formed as products.

• The final substances are called reactants.

• Bonds between atoms are broken and new bonds are formed.

Tags

NGSS.HS-PS1-7

When a scientist mixes two chemicals, an exothermic reaction takes place. Which of the following would be proof that the reaction was exothermic?

• a change of color

• a temperature decrease

• a change of state

• a temperature increase

Tags

NGSS.HS-PS1-4

Which of the following describes a precipitate?

• liquid forms when a block of metal is heated

• a gas forms when a solid is placed in a liquid

• solid forms when one solution is poured into another

• bubbles form when acid is poured on a rock

Tags

NGSS.MS-PS1-2

Tags

NGSS.HS-PS1-1

Which of the following combinations of symbol and explanation of symbol is correct when used in a chemical equation?

• (g), grams

• (l), liters

• (aq), aqueous

• (s) stable

Which of the following is incorrect ?

• An equation is balanced by changing subscripts as needed.

• Chemical equations are balanced to show that matter is conserved.

• Reactants are substances written to the left of the arrow.

• Coefficients indicate the relative number of molecules of each substance in a chemical reaction.

Tags

NGSS.HS-PS1-7

Which observation (a-c) is evidence that a chemical reaction has occurred?

• color change

• bubbles form

• energy is produced

• all choices are indicators that a chemical reaction has occured

Tags

NGSS.MS-PS1-2

To balance a chemical equation, you are allowed to change the __.

• coefficients

• subscripts

• formulas of the products

• formulas of the reactants

In a chemical equation, the symbol (aq) indicates that the substance is

• water

• dissolved in water

• an acid

• insoluble

What does a “Δ” above the arrow in a chemical equation mean?

• a catalyst is needed in the reaction

• a precipitate will form during the reaction

• electricity or light is needed in the reaction

• heat is supplied to the reaction