CHEMICAL EQUATIONS AND REACTIONS

What do chemical equations represent?

Chemical equations represent the reactants and products involved in a chemical reaction.

What is the law of conservation of mass?

Matter cannot be created or destroyed.

Why is balancing chemical equations essential?

To ensure the number of atoms for each element is equal on both sides of the equation.

What does the process of balancing involve?

Adjusting the coefficients of the reactants and products.

How do we know that a chemical reaction has occurred?

Observable changes such as change in color, state, evolution of gas, and change in temperature.

What indicates a change in color during a chemical reaction?

The substances involved change color.

What does a change in state mean?

A substance changes from solid to liquid or liquid to gas.

What does the evolution of gas mean?

Bubbles or fumes appear, indicating gas production.

What is the significance of temperature change in a reaction?

The reaction vessel may become hotter (exothermic) or colder (endothermic).

What is valency?

The combining capacity of an element, often represented by ion charges.

What are cations?

Positive ions with specific valencies.

Give an example of a cation with a valency of +1.

Sodium ($Na^{+1}$).

Provide an example of a cation with a valency of +2.

Calcium ($Ca^{2+}$).

Name a cation that has a valency of +3.

Aluminium ($Al^{3+}$).

What are anions?

Negative ions with specific valencies.

Give an example of an anion with a valency of -1.

Chloride ($Cl^{-1}$).

Provide an example of an anion with a valency of -2.

Sulfate ($SO_4^{2-}$).

What is a combination reaction?

A reaction where two or more reactants combine to form a single product.

Write the equation for the burning of magnesium ribbon.

$2Mg(s) + O_2(g) \rightarrow 2MgO(s) + \text{Heat}$.

What is formed when magnesium burns in air?

Magnesium Oxide ($MgO$) is formed.

What is a key observation when magnesium ribbon burns?

It burns with a dazzling white flame.

Define decomposition reactions.

Reactions where a single reactant breaks down into two or more simpler products.

What are endothermic reactions?

Reactions that require energy to break chemical bonds.

What is thermal decomposition?

Decomposition that uses heat energy.

Write the thermal decomposition equation for Ferrous Sulfate Crystals.

$FeSO_4 \bullet 7H_2O(s) \rightarrow FeSO_4(s) + 7H_2O(g)$.

What gas is produced from the thermal decomposition of Lead Nitrate?

Nitrogen Dioxide ($NO_2$) and Oxygen gas ($O_2$).

What is electrolytic decomposition?

Decomposition that uses electrical energy.

Write the electrolysis equation for water.

$2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$.

What ratio of gases is collected during the electrolysis of water?

The volume ratio of hydrogen to oxygen is 2:1.

Define displacement reactions.

Reactions where a more reactive element displaces a less reactive element from its compound.

What is the reactivity series?

The order of elements based on their reactivity.

Write the displacement equation for Iron Nail in Copper Sulfate.

$Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$.

What happens to copper sulfate when an iron nail is introduced?

The blue color fades to light green as Ferrous Sulfate forms.

What occurs in double displacement reactions?

Exchange of ions between reactants to form new compounds.

Give an example of a precipitation reaction.

$Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$.

What is oxidation?

Gain of oxygen or loss of hydrogen.

What is reduction?

Loss of oxygen or gain of hydrogen.

What is a redox reaction?

A reaction where oxidation and reduction occur simultaneously.

What is corrosion?

The slow eating away of metal surfaces by air, moisture, or chemicals.

What is rancidity?

The oxidation of fats and oils in food, resulting in an unpleasant smell and taste.

Define chemical change.

Results in the formation of new substances and is often irreversible.

What defines a physical change?

No new chemical substances are formed; involves changes in state, shape, or size.

What is the purpose of balancing chemical equations?

To adhere to the law of conservation of mass.

List the steps in the hierarchical balancing method.

1. Balance metals. 2. Balance non-metals. 3. Balance oxygen. 4. Balance hydrogen. 5. Repeat if necessary.

What occurs when iron rusts?

It forms reddish-brown hydrated iron oxide.

What is the mnemonic to remember the indicators of a chemical reaction?

FACTS (Formation of a precipitate, Altered Color, Concentration/Evolution of a Gas, Temperature Change, State Change).

What means does a substance undergo in tarnishing?

It undergoes oxidation.

Explain how silver tarnishes.

Silver reacts with $H_2S$ in the air to form black Silver Sulfide ($Ag_2S$).

Why does an iron nail change color in copper sulfate?

Iron displaces copper, forming Ferrous Sulfate (light green), thus altering the blue color.

What evidence suggests a chemical reaction during electrolysis?

Bubbles form indicating the release of gases.

What is the reaction type of burning magnesium in oxygen?

It is both a combination reaction and an exothermic reaction.

What role does magnesium oxide play when cleaning magnesium ribbon?

It protects the surface from burning effectively unless removed.

What change occurs in color during the electrolysis of water?

No direct color change is observed in pure water.

How does the visual appearance of Copper change after displacement?

Copper deposits appear as reddish-brown on the iron nail.

What happens to the temperature of the reaction vessel in an exothermic reaction?

The temperature increases.

What happens during the formation of slaked lime?

Quick Lime reacts with water producing calcium hydroxide and heat.

What is an example of an endothermic reaction?

Thermal decomposition reactions generally require energy input.

What is the primary focus of chemical equation balancing?

To ensure mass is conserved.

What does the term 'precipitate' refer to?

An insoluble solid formed during a chemical reaction.

Where do oxidation and reduction occur in redox reactions?

Oxidation occurs at the reducing agent and reduction at the oxidizing agent.

What is a characteristic observation during the electrolysis of water?

Hydrogen collects at the cathode while oxygen collects at the anode.

What reaction does the electrolysis of water demonstrate?

Decomposition reaction using electricity.

Name a common application of photochemical reactions.

Used in black and white photography.

How can you prevent rancidity in food?

By adding antioxidants, storing in airtight containers, or flushing with nitrogen gas.

How does the reactivity series help in displacement reactions?

It determines if one element can displace another from its compound.

What describes a chemical reaction in terms of physical characteristics?

Observable changes such as color change, gas evolution, and temperature change.

Why is dry storage essential for silver halides?

To prevent accidental decomposition by light.

Why is magnesium ribbon shiny after cleaning?

The clean surface allows for efficient burning in the presence of oxygen.

What observation characterizes the decomposition of silver chloride?

White silver chloride turns grey upon light exposure.

Identify the effects of a substance losing electrons in a reaction.

It undergoes oxidation and increases its oxidation state.

Identify the effects of a substance gaining electrons in a reaction.

It undergoes reduction and decreases its oxidation state.

What is a common characteristic of exothermic reactions?

They release heat.

Give an example of an endothermic process in daily life.

Photosynthesis in plants.

How do ionic charges relate to compound formation?

Ionic charges determine how ions combine to form neutral compounds.

What does the equation $2AgBr(s) \rightarrow 2Ag(s) + Br_2(g)$ represent?

Photochemical decomposition of silver bromide under sunlight.

Why are some ions called inert in reactions?

They do not readily participate in chemical reactions.

What is the strain on the beaker when slaked lime formation occurs?

High heat generation from the vigorous reaction with water.

Mention a key factor that affects how quickly a reaction occurs.

The surface area of reactants can influence reaction speed.

What is one identifying factor in thermal decomposition reactions?

They may produce gases as a product.

How do bond energies relate to chemical reactions?

Breaking bonds requires energy; forming bonds releases energy.

What role do catalysts play in chemical reactions?

They speed up reactions without being consumed.

How does temperature affect reaction rates?

Higher temperatures generally increase reaction rates.

What happens to the stability of products in exothermic reactions?

Products are typically more stable than reactants.

What is the role of the reducing agent in a redox reaction?

It donates electrons and reduces another species.

What does the formula $Ca(OH)_2(aq) + CO_2(g) \rightarrow CaCO_3(s) + H_2O(l)$ demonstrate?

Formation of calcium carbonate from slaked lime and carbon dioxide.