Chemistry Test 4- Evidence of Chemical Reactions 1

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? A. A test tube becomes cool to the touch. B. A liquid appears to glow. C. A new odor comes from a beaker. D. A solid forms from a mixture of solutions.

A. A test tube becomes cool to the touch.

The images show two unrelated events occurring at separate times. mc026-1.jpgmc026-2.jpg Which event is most likely an example of a chemical reaction? A. Event 1 because there is a color change. B. Event 1 because there is a release of heat and light. C. Event 2 because the temperature is dropping in the liquid. D. Event 2 because the blue color mixes throughout the liquid.

A. Event 1 because there is a color change.

A piece of limestone erodes due to acid rain. This process can be best described as a A. slow chemical change. B. rapid chemical change. C. slow physical change. D. rapid physical change.

A. slow chemical change.

During an experiment, a student observes the formation of a precipitate. Why does this indicate that a chemical reaction is likely occurring? A. A solid forms, and there is a change of color. B. A gas forms, and there is a change of color. C. A solid forms, and light is emitted. D. A gas forms, and light is emitted.

A. A solid forms, and there is a change of color.

Which statement describes a chemical reaction? A. Atoms in the products are rearranged to form new substances. B. Atoms in the reactants are rearranged to form new substances. C. Atoms in the products change into new atoms to form new substances. D. Atoms in the reactants change into new atoms to form new substances.

B. Atoms in the reactants are rearranged to form new substances.

Which is the most important question for deciding if a chemical reaction has occurred? A. Was there a change in the size? B. Was any heat energy given off? C. What is the density of the substance? D. What is the texture of the substance?

B. Was any heat energy given off?

Which indicator most likely suggests that a chemical change is taking place? A. change in size B. change of color C. change of state D. change in shape

B. change of color

When sodium metal is added to water, an orange flame is observed on the metal surface. Based on this observation, what can best be concluded? A. A physical change occurs because the metal gets smaller. B. A chemical reaction occurs because the liquid becomes cloudy. C. A chemical reaction occurs because heat and light are given off. D. A physical change occurs because vapor is released into the air.

C. A chemical reaction occurs because heat and light are given off.

Two different liquids are mixed together. Which observation indicates that an exothermic chemical reaction has taken place? A. an increase in volume B. a decrease in volume C. a rise in temperature D. a drop in temperature

C. A rise in temperature

Burning a piece of wood in fire can be best described as a A. chemical change because the atoms in wood change their state. B. physical change because the atoms in wood are turned into a gaseous product. C. chemical change because the atoms in wood and oxygen are rearranged. D. physical change because the atoms in wood are turned into black ash.

C. Chemical change because the atoms in wood and oxygen are rearranged.

The chemical formula below shows how salt is produced. HCl + NaOH ------> NaCl + H2O Which substances are the reactants? A. HCl and NaCl B. NaCl and H2O C. HCl and NaOH D. NaOH and H2O

C. HCl and NaOH

A solid is placed in a solution. Which observation most likely indicates that a chemical reaction has occurred? A. The size of the solid has rapidly decreased. B. The color of the solution has not changed. C. The solid has bubbles forming on its surface. D. The temperature of the solution stays the same.

C. The solid has bubbles forming on its surface.

Among these processes, which is the slowest chemical reaction? A. digesting food B. boiling an egg C. tarnishing of silver D. melting of a glacier

C. tarnishing of silver

Which statement about a chemical reaction is true? A. It occurs only at low temperatures. B. It occurs only at high temperatures. C. It occurs whenever a physical change takes place. D. It occurs whenever a chemical change takes place.

D. It occurs whenever a chemical change takes place.