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Matter and Chemical Change - Physical vs. Chemical Changes

Grade 7IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Matter is anything that has mass and takes up space, consisting of particles like atoms and molecules (e.g., H2OH_{2}O or O2O_{2}).

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A Physical Change is a change in the state or appearance of matter without changing its chemical composition. These are usually reversible. Examples include melting ice (H2O(s)→H2O(l)H_{2}O(s) \rightarrow H_{2}O(l)) or dissolving sugar in water.

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A Chemical Change occurs when substances react to form new substances with different properties. This involves the breaking and forming of chemical bonds, such as 2H2+O2→2H2O2H_{2} + O_{2} \rightarrow 2H_{2}O.

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Indicators of a chemical change include: unexpected color change, temperature change (release or absorption of energy ΔH\Delta H), production of a gas (effervescence), or the formation of a solid precipitate.

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The Law of Conservation of Mass states that in any physical or chemical change, the total mass of the system remains constant: ∑mreactants=∑mproducts\sum m_{reactants} = \sum m_{products}.

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Particle Theory explains that in physical changes, the arrangement of particles changes, while in chemical changes, the atoms are rearranged to form new molecules.

📐Formulae

Massreactants=MassproductsMass_{reactants} = Mass_{products}

Density(D)=mVDensity (D) = \frac{m}{V}

Csolid+O2(g)→CO2(g)C_{solid} + O_{2(g)} \rightarrow CO_{2(g)}

ΔT=Tfinal−Tinitial\Delta T = T_{final} - T_{initial}

💡Examples

Problem 1:

A student mixes 10g10g of baking soda (NaHCO3NaHCO_{3}) with 50g50g of vinegar (CH3COOHCH_{3}COOH) in a sealed flask. After the reaction, a gas is produced. What is the total mass of the contents in the flask?

Solution:

60g60g

Explanation:

According to the Law of Conservation of Mass, the total mass before the reaction (10g+50g=60g10g + 50g = 60g) must equal the total mass after the reaction, regardless of the chemical change and the production of CO2CO_{2} gas, because the flask is sealed.

Problem 2:

Identify the type of change: Iron (FeFe) reacting with oxygen (O2O_{2}) to form rust (Fe2O3Fe_{2}O_{3}).

Solution:

Chemical Change

Explanation:

This is a chemical change because a new substance (iron oxide) is formed with different chemical properties than the original iron and oxygen. This is represented by the equation: 4Fe+3O2→2Fe2O34Fe + 3O_{2} \rightarrow 2Fe_{2}O_{3}.

Problem 3:

Is the boiling of water (H2O(l)→H2O(g)H_{2}O(l) \rightarrow H_{2}O(g)) a physical or chemical change?

Solution:

Physical Change

Explanation:

Boiling is a change of state. The molecules remain H2OH_{2}O throughout the process; only the distance and energy between the particles change. No new chemical substance is created.