Characteristics of Chemical Reactions

Questions and Answers

What characterizes the chemical reaction between quicklime and water?

Absorption of a lot of heat energy

A fall in the reaction mixture temperature

The production of a solid precipitate

An increase in the reaction mixture temperature (correct)

Which of the following reactions is endothermic?

Reaction between barium hydroxide and ammonium chloride (correct)

Reaction between quicklime and water

Reaction between zinc granules and dilute sulfuric acid

Burning of carbon in air

When zinc granules react with dilute sulfuric acid, the temperature of the reaction mixture:

Fluctuates

Falls gradually

Rises (correct)

Remains constant

What is formed when quicklime reacts with water?

Calcium hydroxide Signup and view all the answers

Which chemical reaction involves the release of hydrogen gas?

Reaction between zinc and dilute sulfuric acid Signup and view all the answers

Which reaction mixture becomes very cold due to heat absorption?

Barium hydroxide and ammonium chloride Signup and view all the answers

Why does the temperature rise when burning carbon in air?

A lot of heat is released Signup and view all the answers

Which of the following reactions involves the formation of barium chloride, ammonia, and water?

Reaction between barium hydroxide and ammonium chloride Signup and view all the answers

What is the immediate observable change when potassium iodide solution is added to lead nitrate solution in a test tube?

Formation of a yellow precipitate Signup and view all the answers

What happens when citric acid reacts with potassium permanganate solution?

Purple color disappears Signup and view all the answers

What is observed when a chemical reaction produces heat energy?

Temperature of the reaction mixture rises Signup and view all the answers

What is the typical effect on temperature when a chemical reaction absorbs heat energy?

Temperature of the reaction mixture falls Signup and view all the answers

Which of the following pairs correctly describes the type of change and the observable effect in the reaction between lead nitrate and potassium iodide?

Change in color: Yellow precipitate forms Signup and view all the answers

Which of the following reactions is characterized by the evolution of hydrogen gas?

Zinc reacting with diluted sulfuric acid. Signup and view all the answers

What type of change is observed when two substances form a precipitate?

Formation of a solid product that separates from the solution. Signup and view all the answers

Which example involves the reaction of an acid with a metal?

Zinc reacting with diluted hydrochloric acid. Signup and view all the answers

Which of the following is NOT an observable characteristic of a chemical reaction?

Increase in solubility. Signup and view all the answers

Which reaction is characterized by the evolution of carbon dioxide gas?

Dilute hydrochloric acid poured over sodium carbonate. Signup and view all the answers

What is observed when potassium iodide is added to a solution of lead nitrate?

Formation of a yellow precipitate. Signup and view all the answers

What indicates the presence of a chemical reaction when zinc reacts with dilute sulfuric acid besides the evolution of hydrogen gas?

Rise in temperature. Signup and view all the answers

Which of the following statements is true regarding the formation of a precipitate?

A precipitate is an insoluble solid that forms during a chemical reaction. Signup and view all the answers

Which of the following statements correctly defines a balanced chemical equation?

A balanced chemical equation has equal atoms of all elements in the reactants and products. Signup and view all the answers

Why is the given equation: H2 + O2 → H2O, considered unbalanced?

The number of oxygen atoms is unequal in reactants and products. Signup and view all the answers

In the balanced chemical equation 'Zn + H2SO4 → ZnSO4 + H2', how many atoms of oxygen are present in the products?

4 Signup and view all the answers

Which law is being followed when the atoms in the reactants are equal to the atoms in the products in a chemical reaction?

Law of Conservation of Mass Signup and view all the answers

Which pair of reactants and their corresponding products correctly exemplify a balanced chemical equation?

N2 + 3H2 → 2NH3 Signup and view all the answers

Considering the equation H2 + O2 → H2O, how can it be balanced?

2H2 + O2 → 2H2O Signup and view all the answers

Which of the following is a characteristic of a balanced chemical equation?

Equal atoms on both sides Signup and view all the answers

What does the equation 'Zn + H2SO4 → ZnSO4 + H2' demonstrate about the reaction?

The atoms are conserved during the reaction. Signup and view all the answers

What is a characteristic of the combustion reaction of candle wax?

Change in state from solid to gas Signup and view all the answers

Which substances are the products of the reaction between zinc and sulphuric acid?

Zinc sulphate and hydrogen Signup and view all the answers

In the reaction between potassium iodide and lead nitrate solution, which characteristics are observed?

Formation of a precipitate and color change Signup and view all the answers

According to the balanced chemical equation for the reaction of zinc and sulphuric acid, how many hydrogen atoms are found in the reactants?

2 Signup and view all the answers

What is represented by the arrow (→) in a chemical equation?

Combination of reactants to form products Signup and view all the answers

Which of the following reactions shows both a change in temperature and evolution of gas?

Reaction of zinc with dilute sulphuric acid Signup and view all the answers

Which equation correctly represents the symbolic form of the reaction between zinc and sulphuric acid?

Zn + H2SO4 → ZnSO4 + H2 Signup and view all the answers

Which characteristic is NOT associated with the reaction between zinc and dilute sulphuric acid?

Formation of a precipitate Signup and view all the answers

What is the symbol and formula of sulphuric acid?

H2SO4 Signup and view all the answers

What is one way a chemical reaction can be represented?

By using symbols and formulae of the substances Signup and view all the answers

What is the key indicator for identifying an exothermic reaction in a chemical equation?

Heat is written on the products' side. Signup and view all the answers

Which of the following is a correct representation of an endothermic reaction?

N2(g) + O2(g) + Heat -> 2NO(g) Signup and view all the answers

Which reaction indicates heat absorption and hence an endothermic reaction?

Formation of nitrogen monoxide from nitrogen and oxygen Signup and view all the answers

What is common among all combustion reactions?

They evolve heat. Signup and view all the answers

Which scenario describes an exothermic process?

Combustion of natural gas Signup and view all the answers

In which of the following conditions would you typically write '+ Heat' on the reactants' side?

When heat is absorbed during the reaction Signup and view all the answers

In the equation $H_2 + O_2 \rightarrow H_2O$, what is the main reason that it is initially unbalanced?

The number of oxygen atoms is unequal on both sides. Signup and view all the answers

After balancing the number of oxygen atoms in the equation $H_2 + O_2 \rightarrow 2H_2O$, what imbalance occurs?

The number of hydrogen atoms becomes unequal. Signup and view all the answers

Which step is required to balance the hydrogen atoms in the equation $H_2 + O_2 \rightarrow 2H_2O$?

Multiplying $H_2$ by 2. Signup and view all the answers

Which of the following is the correctly balanced equation for hydrogen burning in oxygen to form water?

$2H_2 + O_2 \rightarrow 2H_2O$ Signup and view all the answers

What is the definition of balancing an equation in chemistry?

Making the number of atoms of each element equal on both sides. Signup and view all the answers

In which process is the hit and trial method mainly employed?

Balancing chemical equations. Signup and view all the answers

Which of the following combination represents the reactants in the equation $2H_2 + O_2 \rightarrow 2H_2O$?

$H_2$ and $O_2$ Signup and view all the answers

In the final balanced equation $2H_2 + O_2 \rightarrow 2H_2O$, what are the coefficients of $H_2$ and $O_2$, respectively?

2 and 1 Signup and view all the answers

What does the symbol (aq) represent in a chemical equation?

An aqueous solution Signup and view all the answers

Which of the following equations represents the reaction of calcium hydroxide with carbon dioxide?

Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l) Signup and view all the answers

What is indicated by the symbol (s) in a chemical equation?

Solid state Signup and view all the answers

Which of the following enhances the informativeness of a chemical equation?

Indicating the physical states of reactants and products Signup and view all the answers

What product is formed as a precipitate when calcium hydroxide reacts with carbon dioxide?

Calcium carbonate Signup and view all the answers

Which state symbol is correctly matched with its meaning?

(g) - Gaseous state Signup and view all the answers

How many hydrogen atoms are present in the products of the balanced equation for the reaction between hydrogen and chlorine?

2 Signup and view all the answers

What does the chemical equation 'Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)' illustrate?

Reactants and products in different physical states Signup and view all the answers

What does the symbol (l) indicate in a chemical equation?

Liquid state Signup and view all the answers

What are the state symbols for the reactants and products in the balanced equation of iron reacting with steam?

Fe(s), H2O(g), Fe3O4(s), H2(g) Signup and view all the answers

Which equation shows the formation of a precipitate?

Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l) Signup and view all the answers

In the balanced equation of the reaction between hydrogen and nitrogen to form ammonia, how many molecules of ammonia are produced?

2 Signup and view all the answers

For a reaction to be in a balanced state, what must be equal on both sides?

Number of atoms of each element Signup and view all the answers

Which of the following correctly balances the equation for hydrogen reacting with chlorine?

H2 + Cl2 → 2HCl Signup and view all the answers

What is the formula of iron (II, III) oxide?

Fe3O4 Signup and view all the answers

In the reaction between hydrogen and nitrogen to form ammonia, what is the stoichiometric coefficient of hydrogen in the balanced equation?

3 Signup and view all the answers

How many iron atoms are present on both sides of the balanced equation for the reaction between iron and steam?

3 Signup and view all the answers

When balancing the equation for the reaction of hydrogen with nitrogen to form ammonia, which molecule is adjusted last?

NH3 Signup and view all the answers

What type of reaction is the decomposition of calcium carbonate?

Endothermic reaction Signup and view all the answers

Which conditions are necessary for the photosynthesis reaction to occur?

Sunlight and chlorophyll Signup and view all the answers

Which of the following equations correctly represents the decomposition of potassium chlorate using a catalyst?

2KClO2 (s) MnO2 → 2KCl (s) + 3O2 (g) Signup and view all the answers

Which of the following is an endothermic reaction?

Electrolysis of water Signup and view all the answers

What pressure and temperature conditions are required for the production of methanol from carbon monoxide and hydrogen?

300 atm and 300°C Signup and view all the answers

What is the catalyst used in the production of methanol from carbon monoxide and hydrogen?

A mixture of zinc oxide and chromium oxide Signup and view all the answers

Which gas is produced alongside potassium chloride when potassium chlorate decomposes?

Oxygen Signup and view all the answers

What is indicated by the delta (Δ) sign over the arrow in a chemical equation?

The requirement of heat Signup and view all the answers

Study Notes

Characteristics of Chemical Reactions

A chemical reaction involves the conversion of reactants into products.
Characteristics of chemical reactions include:
Evolution of a gas
Formation of a precipitate
Change in color
Change in temperature
Change in state

Evolution of a Gas

Some chemical reactions are characterized by the evolution of a gas.
Examples:
Reaction between zinc and dilute sulfuric acid to produce hydrogen gas
Reaction between sodium carbonate and dilute hydrochloric acid to produce carbon dioxide gas

Formation of a Precipitate

A precipitate is a solid product that separates out from a solution during a chemical reaction.
Examples:
Reaction between potassium iodide solution and lead nitrate solution to form a yellow precipitate of lead iodide

Change in Colour

Some chemical reactions are characterized by a change in colour.
Example:
Reaction between citric acid and potassium permanganate, where the purple colour of the potassium permanganate solution disappears

Change in Temperature

Chemical reactions can produce or absorb heat energy.
Examples:
Reaction between quicklime and water, where heat is produced and the temperature rises
Reaction between barium hydroxide and ammonium chloride, where heat is absorbed and the temperature falls

Change in State

Some chemical reactions are characterized by a change in state.
Example:
Combustion reaction of wax, where the physical state changes from solid to liquid and gas

Chemical Equations

A chemical equation is a method of representing a chemical reaction using symbols and formulae of the substances involved.
The reactants are written on the left-hand side of the equation, and the products are written on the right-hand side.
The arrow sign (→) points from the reactants to the products.

Balanced and Unbalanced Chemical Equations

A balanced chemical equation has an equal number of atoms of each element on both sides of the equation.
An unbalanced chemical equation does not have an equal number of atoms of each element on both sides of the equation.
Examples:
Balanced equation: Zn + H2SO4 → ZnSO4 + H2
Unbalanced equation: H2 + O2 → H2O

Balancing of Chemical Equations

The process of making the number of atoms of each element equal on both sides of the equation is called balancing.
Methods of balancing include:
Hit and trial method
Counting the number of atoms of each element on both sides of the equation

Making Equations More Informative

Chemical equations can be made more informative by:
Indicating the physical states of the reactants and products
Indicating the heat changes taking place in the reaction
Indicating the conditions under which the reaction takes place

Physical States of Reactants and Products

The physical states of reactants and products can be indicated using symbols such as (s) for solid, (l) for liquid, (aq) for aqueous solution, and (g) for gas.

Heat Changes in an Equation

Reactions can be classified as exothermic or endothermic based on the heat changes involved.
Exothermic reactions evolve heat, while endothermic reactions absorb heat.
Examples:
Exothermic reaction: C(s) + O2(g) → CO2(g) + Heat
Endothermic reaction: N2(g) + O2(g) + Heat → 2NO(g)

Conditions Under Which the Reaction Takes Place

The conditions under which the reaction takes place can be indicated in the equation using symbols such as Δ for heat, and the symbol or formula of the catalyst.
Examples:
2KClO2(s) Δ MnO2 → 2KCl(s) + 3O2(g)### Chemical Equations and Reactions
The production of methanol involves the reaction: CO (g) + 2H2 (g) → CH3OH (l) at 300 atm and 300°C.

Photosynthesis

Green plants produce food through photosynthesis, combining carbon dioxide with water in the presence of sunlight and chlorophyll to form glucose and oxygen.

Balanced Chemical Equations

A balanced equation has an equal number of atoms of each type in the reactants and products.
Example: 3Fe (s) + 4H2O (g) → Fe3O4 (s) + 4H2 (g)

Writing Balanced Equations

Start with a word equation and replace the words with chemical formulas.
Example: Hydrogen + Chlorine → Hydrogen chloride becomes H2 + Cl2 → HCl
Balance the equation by multiplying the formulas of the reactants or products to get an equal number of atoms on both sides.
Example: H2 + Cl2 → HCl becomes H2 + Cl2 → 2HCl

Sample Problems

Hydrogen gas combines with chlorine to form hydrogen chloride: H2 (g) + Cl2 (g) → 2HCl (g)
Hydrogen gas combines with nitrogen to form ammonia: 3H2 + N2 → 2NH3

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Description

Learn about the characteristics of chemical reactions, including the evolution of a gas, formation of a precipitate, change in color, change in temperature, and change in state.