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States of Matter - Physical vs. Chemical Changes

Grade 6IB

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. It exists primarily in three states: Solid, Liquid, and Gas, defined by the arrangement and energy of particles.

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A Physical Change involves a change in the physical properties of a substance (such as size, shape, or state) without changing its chemical identity. These are often reversible. Example: Melting ice (H2O(s)→H2O(l)H_2O(s) \rightarrow H_2O(l)).

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A Chemical Change results in the formation of one or more new substances with different chemical properties. These changes involve breaking and forming chemical bonds and are usually difficult to reverse. Example: Burning magnesium (2Mg+O2→2MgO2Mg + O_2 \rightarrow 2MgO).

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

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The Law of Conservation of Mass states that in any physical or chemical change, the total mass of the substances involved remains constant. The mass of the reactants must equal the mass of the products: mreactants=mproductsm_{\text{reactants}} = m_{\text{products}}.

📐Formulae

Density(ρ)=Mass(m)Volume(V)\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}

Total Massbefore=Total Massafter\text{Total Mass}_{\text{before}} = \text{Total Mass}_{\text{after}}

H2O(s)→meltingH2O(l)→boilingH2O(g)H_2O(s) \xrightarrow{\text{melting}} H_2O(l) \xrightarrow{\text{boiling}} H_2O(g)

💡Examples

Problem 1:

Identify the type of change occurring when a piece of paper is burned to form ash and smoke (C+O2→CO2C + O_2 \rightarrow CO_2).

Solution:

Chemical Change

Explanation:

The original substance (cellulose/carbon) reacts with oxygen (O2O_2) to create new substances, carbon dioxide (CO2CO_2) and ash. This process is irreversible and involves the release of energy in the form of heat and light.

Problem 2:

An ice cube with a mass of 10g10g melts in a sealed container. What is the mass of the resulting liquid water?

Solution:

10g10g

Explanation:

According to the Law of Conservation of Mass, mass is not lost during a physical change. The state changes from solid (H2O(s)H_2O(s)) to liquid (H2O(l)H_2O(l)), but the number of molecules remains the same.

Problem 3:

Is dissolving sugar (C12H22O11C_{12}H_{22}O_{11}) into water a physical or chemical change?

Solution:

Physical Change

Explanation:

Dissolving is a physical change because the sugar molecules spread out within the water but do not transform into a new chemical substance. The sugar can be recovered by evaporating the water (H2OH_2O).