Chemical Reactions Observations

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Questions and Answers

What indicates that a chemical reaction has occurred?

Change in temperature (correct)

Change in shape

No evolution of gas

No change in color

Which type of equation shows the change from reactants to products?

Arithmetical equation

Symbolic equation

Chemical reaction equation

Word-equation (correct)

In the reaction between magnesium and oxygen, which of the following is the product?

Oxygen

Hydrogen

Magnesium oxide (correct)

Magnesium

What is shown on the left-hand side of a word-equation?

Reactants with plus signs Signup and view all the answers

Which of the following does NOT suggest a chemical reaction has occurred?

Physical mixing of substances Signup and view all the answers

What term describes the substances that undergo change in a chemical reaction?

Reactants Signup and view all the answers

In a reaction, what does the arrow in a word-equation represent?

The direction of the reaction Signup and view all the answers

How is the reaction of magnesium burning in oxygen expressed in word-equation form?

Magnesium + Oxygen → Magnesium oxide Signup and view all the answers

What type of reaction occurs when ferrous sulphate decomposes upon heating?

Decomposition reaction Signup and view all the answers

Which of the following is NOT a product of the thermal decomposition of ferrous sulphate?

Calcium oxide (CaO) Signup and view all the answers

What happens to the ferrous sulphate crystals when heated?

They change color and lose water. Signup and view all the answers

What is a common use of calcium oxide produced from the decomposition of calcium carbonate?

Manufacturing cement Signup and view all the answers

During the thermal decomposition of lead nitrate, which gas is emitted?

Nitrogen dioxide (NO2) Signup and view all the answers

The process of heating to induce decomposition reactions is referred to as what?

Thermal decomposition Signup and view all the answers

Which of the following is a characteristic of decomposition reactions?

They break down a single reactant into simpler products. Signup and view all the answers

Which of the following statements about the decomposition of calcium carbonate is true?

It results in the formation of calcium oxide and carbon dioxide. Signup and view all the answers

In the reaction CuO + H2 → Cu + H2O, what occurs to copper(II) oxide?

It is reduced. Signup and view all the answers

What defines an oxidation-reduction (redox) reaction?

One reactant is reduced while the other is oxidised. Signup and view all the answers

During the reaction ZnO + C → Zn + CO, what happens to carbon?

It is oxidised to CO. Signup and view all the answers

What happens to manganese dioxide (MnO2) in the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2?

It is reduced to MnCl2. Signup and view all the answers

When a substance gains oxygen during a reaction, what is it said to undergo?

Oxidation. Signup and view all the answers

What occurs during the rusting of iron?

Iron is oxidised to form a reddish brown coating. Signup and view all the answers

What is the green coating formed on copper due to corrosion?

Copper patina. Signup and view all the answers

What effect does gaining hydrogen have on a substance in a chemical reaction?

It is reduced. Signup and view all the answers

What is the correct number of hydrogen molecules needed to balance the equation in the first step?

4 molecules of H2 Signup and view all the answers

After balancing hydrogen atoms, what element remains to be balanced in the equation?

Iron Signup and view all the answers

How many atoms of iron are initially present in the reactants for balancing?

1 Signup and view all the answers

What is the balanced equation that results after all elements are balanced?

3 Fe + 4 H2O → Fe3O4 + 4 H2 Signup and view all the answers

What method is employed for balancing the chemical equations as discussed?

Hit-and-trial method Signup and view all the answers

Which physical state is represented by the symbol (aq) in chemical equations?

Aqueous solution Signup and view all the answers

What notation is used to indicate a substance in the gaseous state in a chemical equation?

(g) Signup and view all the answers

Why is it important to mention the physical states of reactants and products in a chemical equation?

To make the equation more informative Signup and view all the answers

Which statement about the reaction 2PbO(s) + C(s) → 2Pb(s) + CO2(g) is correct?

Lead is getting oxidised. Signup and view all the answers

What type of reaction is represented by Fe2O3 + 2Al → Al2O3 + 2Fe?

Displacement reaction. Signup and view all the answers

When dilute hydrochloric acid is added to iron fillings, what products are formed?

Hydrogen gas and iron chloride. Signup and view all the answers

Which of the following correctly describes oxidation?

Gain of oxygen. Signup and view all the answers

Why should chemical equations be balanced?

To ensure mass is conserved. Signup and view all the answers

What is produced when calcium hydroxide reacts with carbon dioxide?

Calcium carbonate and water. Signup and view all the answers

Which of these equations is correctly balanced?

HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O. Signup and view all the answers

What is the product of the reaction between zinc and silver nitrate?

Zinc nitrate and silver. Signup and view all the answers

Study Notes

Observations of Chemical Reactions

Changes indicating a chemical reaction include: change in state, color shift, gas evolution, and temperature change.
Various chemical reactions occur in daily life, prompting a study of their types and symbolic representations.

Chemical Equations

A chemical reaction can be expressed through word equations that summarize the transformation of reactants to products, e.g.:
- Magnesium + Oxygen → Magnesium oxide
Reactants are listed on the left and products on the right, separated by an arrow.

Balancing Chemical Equations

Balancing ensures the number of atoms for each element remains equal on both sides of the equation.
Initial equations may require balancing through trial and adjustments using smallest whole number coefficients.
Use of symbols for physical states enhances chemical equations:
- (g) for gas, (l) for liquid, (aq) for aqueous, (s) for solid.

Types of Reactions

Decomposition reactions involve a single reactant breaking down into simpler products, e.g.,:
- CaCO3(s) → CaO(s) + CO2(g)
Thermal decomposition requires heat, illustrated through various examples.

Redox Reactions

Oxidation involves the gain of oxygen or loss of hydrogen; reduction involves the loss of oxygen or gain of hydrogen.
In reaction dynamics, one reactant is oxidized while another is reduced, classified as redox reactions.
Examples include:
- CuO + H2 → Cu + H2O

Corrosion and Its Effects

Corrosion often manifests as rusting in iron and tarnishing in metals like copper and silver, affecting their appearance.
Oxidation-reduction reactions also characterize processes of corrosion.

Exercises on Chemical Reactions

Understand and identify incorrect statements regarding specific reactions.
Recognize different reaction types (combination, displacement, decomposition) through provided examples.

Practice with Chemical Equations

Translate statements into chemical equations, ensuring to balance them accurately.
Familiarize with balancing techniques and identify types of reactions, enhancing overall comprehension of chemical processes.

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Description

This quiz explores the observations that indicate a chemical reaction has taken place, including changes in temperature, state, and color. Participate to test your understanding of the key signs of chemical reactions.