Chemical Reactions Overview and Indicators

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Questions and Answers

Why are the properties of water different than the reactant gases?

The properties of the gases are combined to give water its properties.

The difference in the properties of water can be attributed to physical changes to the hydrogen and oxygen atoms on a subatomic level.

When substances chemically combine, products with completely different properties form. (correct)

How would you explain the reaction between sodium and chlorine?

When substances combine to form new substances, the properties of the reactants are preserved.

When substances combine to form new substances, the properties of the resulting substances will be different than those of the reactants. (correct)

Sodium and chlorine become different elements during the reaction.

Select the true statement:

Bonds are broken and new bonds are formed during physical changes only.

Bonds are broken and new bonds are formed during chemical reactions only. (correct)

Bonds do not change in either chemical reactions or physical changes.

Which of the following may signal that a new substance has formed?

All of these are correct. Signup and view all the answers

Why are numbers placed before the elements and molecules in a chemical equation?

To balance the equation so that it has the same number of atoms of each element on each side. Signup and view all the answers

Identify the reactant(s) of the following chemical reaction: $4 ext{Ag} + 2 ext{H}_2 ext{S} + ext{O}_2 → 2 ext{Ag}_2 ext{S} + 2 ext{H}_2 ext{O}$

Silver, oxygen and hydrogen sulfide Signup and view all the answers

In a chemical equation, what does the symbol '⇄' mean?

The reaction is reversible and can go in both directions. Signup and view all the answers

Which of the following describes the Law of Conservation of Mass?

The mass of the products equals the mass of the reactants. Signup and view all the answers

Identify the product(s) in the following chemical reaction: $Cr_2O_3 + 3C → 2Cr + 3CO$

Chromium and carbon monoxide Signup and view all the answers

In a chemical reaction, which of the following is true of the products?

The products retain the same number of atoms as the reactants. Signup and view all the answers

Complete the following sentence: 'During a chemical reaction:'

A new substance(s) with the same number of atoms as the initial substance(s) is formed. Signup and view all the answers

What kind of reaction is happening inside the cold pack used for an athlete's injury?

Endothermic Signup and view all the answers

Which statement about energy and chemical reactions is true?

Some chemical reactions absorb and some release energy. Signup and view all the answers

What type of reaction occurs when a cold pack becomes cold after squeezing?

Endothermic Signup and view all the answers

Mixing hydrochloric acid and sodium hydroxide is an example of an exothermic reaction. This means:

Energy is released during the chemical reaction. Signup and view all the answers

Study Notes

Chemical Reactions Overview

Liquid water (H2O) is formed from the reaction of hydrogen (H2) and oxygen (O2); properties differ due to new substance formation.
Sodium (Na) is a reactive solid, and chlorine (Cl), a toxic gas, combine to form stable table salt (NaCl); properties of the new substance differ from reactants.
Chemical reactions involve breaking and forming bonds; this occurs exclusively during chemical changes, not physical changes.

Indicators of Chemical Reactions

Formation of a solid from liquids, color changes, and gas bubbles indicate new substances are forming.
Equations balance to ensure equal numbers of atoms for each element on both sides.

Understanding Chemical Equations

Reactants in the reaction 4 Ag + 2 H2S + O2 → 2 Ag2S + 2 H2O are silver, oxygen, and hydrogen sulfide.
The symbol "⇄" in a chemical equation indicates that the reaction is reversible.
The Law of Conservation of Mass states that the mass of the products equals the mass of the reactants; mass remains constant.

Products of Chemical Reactions

In the reaction Cr2O3 + 3 C → 2 Cr + 3 CO, the products are chromium and carbon monoxide.
Products maintain the same number of atoms as reactants and may form new substances.

Characteristics of Chemical Reactions

A new substance is formed during a chemical reaction, retaining the same number of atoms as the starting materials.
An endothermic reaction occurs in scenarios like cold packs; these absorb energy during the process.
Energy dynamics vary; some reactions absorb energy while others release it, such as in exothermic reactions.

Practical Applications

Cold packs utilize ammonium nitrate and water; breaking barriers initiates an endothermic reaction, creating a cooling effect on injuries.
Mixing hydrochloric acid and sodium hydroxide exemplifies an exothermic reaction where energy is released.

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Description

Explore the principles of chemical reactions, including examples like the formation of water and table salt. Understand the indicators of chemical reactions and the importance of balancing chemical equations according to the Law of Conservation of Mass.