Untitled Quiz

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Questions and Answers

What is the primary factor that determines the chemical energy stored in a molecule?

The energy of all the bonds it contains (correct)

The temperature of the environment

The number of atoms in the molecule

The phase of the substance (solid, liquid, gas)

What occurs during a chemical reaction that causes changes in energy?

Both bonds are broken and new bonds are formed (correct)

Only old bonds are rearranged without forming new ones

Bonds are created without breaking any

Energy remains constant regardless of bond changes

What evidence indicates that a reaction is exothermic?

Emission of sound waves

Absorption of visible light

A decrease in temperature of the surroundings

An increase in temperature of the surroundings (correct)

Which statement is true regarding exothermic and endothermic reactions?

Reaction rates are independent of whether the reaction is exothermic or endothermic (D) Signup and view all the answers

What describes an endothermic reaction?

It absorbs heat from the surroundings. (D) Signup and view all the answers

Which of the following factors does NOT increase the rate of a chemical reaction?

Lowering concentration of reactants (B) Signup and view all the answers

What is the relationship between the energies of bonds that break and bonds that form during a chemical reaction?

Energy released or gained is the difference between the two. (A) Signup and view all the answers

Which scenario best illustrates a fast chemical reaction?

Burning of methane in oxygen (A) Signup and view all the answers

How does temperature affect the rate of a chemical reaction?

Higher temperatures increase the speed of reactions. (C) Signup and view all the answers

What happens to the rate of reaction when the particle size of reactants is decreased?

The reaction rate increases. (C) Signup and view all the answers

Which statement describes the outcomes of chemical changes?

Chemical changes result in the formation of new substances. (A) Signup and view all the answers

When some chemical reactions release energy, what form can this energy take?

As heat and light. (A) Signup and view all the answers

In what way do the chemical properties of reactants differ from those of the products?

They indicate a chemical reaction has occurred. (D) Signup and view all the answers

What is an example of how chemists have increased the diversity of matter?

By inventing plastics that do not exist in nature. (D) Signup and view all the answers

What is defined as the process in which atoms in given substances rearrange into new substances?

Chemical reaction. (B) Signup and view all the answers

Which option provides evidence of a chemical reaction?

Release of gas. (D) Signup and view all the answers

What indicates a chemical reaction has occurred?

Change in color (B), Change in temperature (C) Signup and view all the answers

In a balanced chemical equation, what must be true about the atoms of each element?

The number of atoms must be equal in both reactants and products. (D) Signup and view all the answers

Why are whole numbers used in chemical equations?

Fractional molecules cannot participate in reactions. (D) Signup and view all the answers

How are the states of matter represented in a chemical equation?

With symbols (C) Signup and view all the answers

Which of the following is NOT a characteristic of a chemical equation?

It indicates the speed of reaction. (C) Signup and view all the answers

What shows that mass is conserved in a chemical reaction?

The total mass of the products equals the total mass of the reactants. (D) Signup and view all the answers

What is required for an ionic equation to represent a reaction?

At least one reactant or product must be an ionic compound in solution. (D) Signup and view all the answers

What is a balanced equation?

An equation where the number of atoms of each element is the same in reactants and products. (D) Signup and view all the answers

Study Notes

Chemical Energy

Chemical energy is stored in chemical bonds.
Amount of chemical energy a molecule stores depends on all the bonds it contains.
Chemical reactions involve changes in energy because bonds are broken and new bonds are formed.
Energy is required to break chemical bonds in reactants, allowing atoms to rearrange.
Energy is released when new chemical bonds form to create products.
The energy released or gained during a chemical reaction is the difference between the energies of the bonds formed and the energies of the bonds broken.

Exothermic and Endothermic Reactions

Exothermic reactions give off heat.
Increased temperature of surroundings is evidence of an exothermic reaction.
Endothermic reactions take in heat.
Reactions cause a decrease in the temperature of their surroundings.

Reaction Rate

Reaction rate measures how fast a reaction occurs.
Concentration of a substance in a mixture is defined as the amount of that substance in a given volume of solution.
A dilute solution has a low concentration of solute, while a concentrated solution has a high concentration of solute.
The reaction between methane and oxygen is an example of a fast chemical reaction.
The reaction between iron and oxygen (rust) is an example of a slow chemical reaction.
Reaction rates vary widely but do not depend on whether a reaction is exothermic or endothermic.

Factors Affecting Reaction Rate

Temperature, particle size, concentration of reactants, and agitation all increase the rate of a reaction.
Increasing the temperature usually increases the rate of a chemical reaction.
For example, cooking food at higher temperatures makes it cook faster, and lower temperatures make it cook slower.
Reactions tend to be faster when the size of the reactant pieces is smaller.
Crushing and cutting reactants decrease particle size and increase contact surface area, speeding up the reaction.
For example, a large log burns slowly because of the limited contact with oxygen, but chopping it into smaller pieces speeds up burning because more wood interacts with oxygen.

Chemical Changes

All chemical changes result in the formation of new substances.
The energy change during a chemical reaction depends on whether heat is released (increases surrounding temperature) or taken in (decreases surrounding temperature).
Light production is evidence of a chemical reaction, as some chemical reactions release energy in the form of light.
Changes in state (solid, liquid, gas) and color provide evidence of a chemical reaction as reactants and products may have different states or colors.
Reactants and products may have similar physical properties, but their chemical properties are different, signifying a chemical reaction.
Chemists have increased the diversity of matter by creating new substances not found in nature, such as plastics.

Chemical Reactions

Chemical changes involve the rearrangement of atoms in given substances into new substances.
Reactants are starting substances that undergo chemical change.
Products are substances resulting from a chemical reaction.
Evidence of a chemical reaction includes temperature changes, light production, change of state, change of color, and change in chemical properties.

Chemical Equations

Chemical equations use chemical formulas to represent reactants on the left side and products on the right side.
Ionic equations can be used when at least one reactant or product is an ionic compound dissolved in water.
A chemical equation is balanced when the number of atoms of each element is equal in reactants and products.
Comparing the total mass of reactants to the total mass of products demonstrates mass conservation in a reaction, as mass does not change during a reaction.
Whole numbers are used to balance chemical equations because fractions of molecules do not react.

Balancing Chemical Equations

Chemical equations represent what happens to particles during a reaction.
Coefficients are added one at a time to balance each element.
2𝐻2 𝑂 → 2𝐻2 + 𝑂2 is the chemical equation for the decomposition of water into hydrogen and oxygen.
Chemical equations provide information about the elements involved, reactants, products, and states of reactants and products.
State symbols are used to indicate the states of reactants and products:
- (s) for solid
- (l) for liquid
- (g) for gas
- (aq) for dissolved in water (aqueous)
𝑍𝑛(𝑠) + 𝐶𝑢+2 (𝑎𝑞) + 𝑆𝑂4−2 (𝑎𝑞) → 𝐶𝑢(𝑠) + 𝑍𝑛+2 (𝑎𝑞) + 𝑆𝑂4−2 (𝑎𝑞) is the ionic equation for the reaction of zinc with copper sulfate.
A balanced equation is a chemical equation where the number of atoms of each element is the same on both sides.
In a balanced chemical equation, the total mass of the products equals the total mass of the reactants.