Evidence of Chemical Reactions assignment and quiz

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 physical change occurs because the metal gets smaller. A chemical reaction occurs because the liquid becomes cloudy. A chemical reaction occurs because heat and light are given off. A physical change occurs because vapor is released into the air.

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

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

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

Explain the difference between the reactants and products of a chemical reaction.

Did your explanation include the following? Reactants are the starting substances and products are the ending substances in a chemical reaction. The atoms in reactants are arranged one way and are rearranged in a different way to form the products (in other words, reactants are chemically different from products). The properties of reactants differ from the properties of products.

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? Event 1 because there is a color change. Event 1 because there is a release of heat and light. Event 2 because the temperature is dropping in the liquid. Event 2 because the blue color mixes throughout the liquid.

Event 1 because there is a color change.

The chemical formula below shows how salt is produced. HCl + NaOH → NaCl + H2O Which substances are the reactants? HCl and NaCl NaCl and H2O HCl and NaOH NaOH and H2O

HCl and NaOH

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

It occurs whenever a chemical change takes place.

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

The solid has bubbles forming on its surface.

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

Was any heat energy given off?

Evaluate each scenario to determine whether it represents a chemical reaction. Baking cake batter: Shredding paper: Twisting metal wire: Newspaper yellowing in the sunlight:

Yes No No Yes

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

a rise in temperature

When mixed together, baking soda and vinegar undergo a chemical reaction. Carbon dioxide, water, and sodium acetate are formed during the reaction. Which of the following is the correct word equation to illustrate this reaction? baking soda + vinegar mc001-1.jpg carbon dioxide + water + sodium acetate baking soda + water mc001-2.jpg carbon dioxide + vinegar + sodium acetate baking soda + vinegar + carbon dioxide + water + sodium acetate

baking soda + vinegar → carbon dioxide + water + sodium acetate

Identify the reactants in this reaction. carbon dioxide, water, and sodium acetate baking soda and vinegar

baking soda and vinegar

Identify the products in this reaction. carbon dioxide, water, and sodium acetate baking soda and vinegar

carbon dioxide, water, and sodium acetate

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

chemical change because the atoms in wood and oxygen are rearranged.

Bread toasting: gas formation color change light emission

color change

In each case of a chemical reaction shown below, state the indicator of the chemical reaction. Identifying Indicators of Chemical Reactions Bread dough rising: gas formation color change light emission

gas formation

In each case of a chemical reaction shown below, state the indicators of the chemical reaction. Check all of the boxes that apply. Identifying Indicators of Chemical Reactions Meat cooking: gas formation color change light emission

gas formation color change

Fireworks exploding: gas formation color change light emission

gas formation color change light emission

Which term best describes the role of hydrogen gas in the formation of a water molecule? catalyst inhibitor product reactant

reactant