Chemical Changes and Reactions

Flashcards for reviewing chemical changes and reactions lecture notes.

What is a chemical reaction?

The process of breaking chemical bonds of reactants and making new bonds to form products.

What is a chemical bond?

The force that holds the atoms of a molecule together.

List conditions necessary for a chemical change.

Mixing (close contact), solution, heat, light, electricity, pressure, catalyst.

What are photochemical reactions?

Chemical reactions that take place by the action of light.

Why are solutions of silver nitrate kept in brown bottles?

They decompose in the presence of light.

What is the function of a catalyst in a chemical reaction?

To accelerate or decelerate the rate of reaction without being consumed.

What is a positive catalyst?

A catalyst that accelerates a reaction.

What are promoters?

Substances that improve the efficiency of a catalyst.

What is a negative catalyst?

A catalyst that retards a reaction.

Define effervescence.

The formation of gas bubbles in a liquid during a reaction.

What is a precipitate?

An insoluble solid substance formed during a chemical reaction.

Describe a direct combination reaction.

Two or more substances combine to form a single substance.

What is another name for a direct combination reaction?

Synthesis

What happens during decomposition?

A compound breaks up into elements or simpler compounds.

What is thermal decomposition?

Decomposition brought about by heat.

What happens when metal bicarbonates decompose?

They give metal carbonate, water vapor, and carbon dioxide.

What products form when metal nitrates decompose on heating?

Varies depending on metal: metal oxide, nitrogen dioxide, and oxygen, or melt and decompose to give metal nitrite and oxygen.

List the products of digestion in the body as examples of decomposition reactions.

Starches decompose into glucose and sugar, proteins into amino acids, and fats/oils into fatty acids.

Explain reversible reactions.

Reactions where the direction of chemical change can be reversed by changing conditions.

What is thermal dissociation?

Simultaneous reversible decomposition reaction brought about only by heat.

Describe a displacement reaction.

A more active element displaces a less active element from its salt solution.

List the two types of double decomposition reactions.

Precipitation and neutralization reactions.

What is a precipitation reaction?

Two compounds in aqueous state react to form an insoluble salt (precipitate).

Define neutralization.

The reaction between an acid and a base that forms salt and water.

What happens in hydrolysis?

Salt and water react to form an acidic or basic solution.

What type of salts undergo hydrolysis?

Salts formed by strong base/weak acid or strong acid/weak base.

What is the result of a salt formed from strong base and weak acid dissolving in water?

Basic solution, turns red litmus blue.

What is the result of a salt formed from strong acid and weak base dissolving in water?

Acidic solution, turns blue litmus red.

Define chemical energy.

Fixed amount of stored energy in a substance, in the form of potential energy.

What are the two main types of chemical reactions based on energy changes?

Exothermic and endothermic.

Describe an exothermic reaction.

A chemical reaction in which heat is given out, causing a rise in temperature.

Describe an endothermic reaction.

A chemical reaction in which heat is absorbed, causing a fall in temperature.

What is a photochemical reaction?

A reaction that occurs with the absorption of light energy.

Give an example of a photochemical reaction.

Photosynthesis: 6CO2 + 12 H2O --light--> C6H12O6 +6 H2O + 602

What is an electrochemical reaction?

A reaction that occurs with the absorption of electrical energy.

Give an example of an electrochemical reaction.

Acidulated water breaks into hydrogen and oxygen with electricity.

What confirms a chemical reaction?

Evolution of gas, change of color, formation of precipitate, change of state.

What is a precipitation reaction?

A reaction in which one of the products formed is an insoluble substance (precipitate).

What is a physical change?

A change in which only the physical properties of a substance get changed, not its chemical composition.

What is a chemical change?

A change in which chemical composition and chemical properties of reacting substances undergo a change.