# مراجعة هيكل امتحان العلوم الصف السابع Inspire الفصل الثاني

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مراجعة هيكل امتحان العلوم الصف السابع Inspire الفصل الثاني

Thermometers To measure the average kinetic energy or speed of the particles in a material a thermometer is used

Temperature scales include Celsius Fahrenheit and Kelvin. The Celsius scale is used by scientists worldwide

The Kelvin was developed to predict at what temperature particles would stop all motion. This temperature, known as absolute zero, would be recorded at O K, if a substance reached O K, the particles would have no movement or kinetic energy. Scientists have not been able to cool any material to O K

Circle the example in each pair that contains the greatest amount of energy. Explain your choice

1. A glass of water at 20t or a glass of water at 800

The higher the temperature. the higher the kinetic energy

aluminium can at an aluminium can at 20'C

The higher the temperature. the higher the kinetic energy,

#### Potential enerqy

Is stored energy due to the interactions between particles or objects

Attraction and Energy: Particles of matter that are close together exert an attractive force on each other. Solid particles are
close to each other and have the greatest force of attraction between particles. Gas particles are apart and have the smallest force of attraction between particles

The potential energy of particles is due to the position of the particles relative to other particles. As particles move farther apart. the attractive forces between the particles decrease as particles move closer together, the attractive forces between the particles The particles that are farther apart have greater potential energy. Gases have more potential energy than liquids or solids

Ex: The bubbles in this carbonated water have more potential energy than the liquid water particles because they are farther apart from one another. The liquid water particles have less potential energy than the gas in the bubbles because they are closer to each other. The state determines the amount of potential energy contained in a substance

Circle the example in each pair that has the greatest amount Of energy. Explain your choice

1. An ice cube at O'C or a

Because the attraction between the between the particles Of an ice cube

#### Lesson 2: Changes in temperature

Lab: growing air

"story Jacques Charles (1745 -1823) was a French scientist who described the relationship between temperature and volume Of a pes. The change in volume car be measured by using a flexible container such as a balloon

Volume-Temperature Law 4

Charles's law that the volume of ages Increases with increasing temperature, the pressure is constant

When the balloon is in cold air, the temperature Of gas inside the

Decrease in temperature

Decrease in the average kinetic energy of particles

Result, the gas particles slow down

They have less energy to overcome the attractive forces between them and begin to get closer together

Fewer particles hit the inside surface Of the balloon

The balloon appears partially deflated, like the gas has escaped

Thermal contraction: Is a decrease in a volume as its temperature decreases, increase in volume as the temperature increases

Thermal expansion: The number of particles does not change during expansion and contraction

Particle size remains the same during expansion and contraction. The volume that the particles take up changes

What happen to state of matter as Temperature

Melting Matter can change state when it gains or loses enough thermal enerKY, when particles speed up, they start to move farther away from each other. Recall that particles in a solid are also held together by As the particles gain more and more thermal energy, they gain enough energy to start to break away from the other particles. This is the melting point Of a substance

As energy is added, solid particles vibrate faster and temperature increases

As particles move farther apart the solid a liquid Temperature remains constant at
the point

Once all particles are in the Equid state, any additional energy increases the speed of the particles. Temperature increases

chemical formulas are used to easily describe the reactants and the products, it's important to use correct chemical formulas. Examine the formation of carbon dioxide below. The product carbon dioxide is written as C02 and not as CO.CO is the formula for carbon monoxide, which is not the same compound as C02

A subscript describes the number Of atoms Of atoms Of an element in a compound

You might think a balanced equation happens automatically when you write the symbols and. formulas for reactants and products. However, this usually is not the case. For example, the reaction between hydrogen (H2) and Oxygen (02) that forms water (H20) is shown below

Because the numbers of each type of atom are not equal, this equation is not balanced. To accurately represent this reaction, the equation needs to be balanced. When you balance a chemical equation, you count the atoms in the reactants and the products and then add
coefficients to balance the number Of atoms

A coefficient is a number placed in front of an element symbol or chemical formula in an equation

What conclusion can you draw from the scientist's observations

( A. new substance was formed, because the formation of a precipitate is evidence that a chemical reaction took place

B. A physical reaction took place, because the physical properties Of the substances
changed

C. The lead nitrate froze when it was added to the potassium iodide, because solids form as a result of freezing

D. The potassium iodide crashed out of solution, because the solution became supersaturated, and no reaction occurred

#### Concentration Revisited

Think of a crowded hallway. Because the concentration of people is higher in the crowded hallway than in an empty hallway, people probably collide more often

Similarly, increasing the concentration of one or more reactants increases collisions
between particles —e More collisions result in a faster reaction rate. When particles are closer together, more collisions occur

#### Conserving Energy

law of conservation of energy states that even though energy is always transferring, energy is not created and energy is not destroyed. Energy is constantly being reused

The laws of conservation of energy and matter apply to both the physical and living
environments. Plants store glucose molecules in their tissues When plants are eaten by animals, energy and matter transfer to the consumer

One way energy can return to the environment isin the form of thermal energy given off by organisms. Another way is when plants and animals die, the energy and matter contained in their tissues is recycled by decomposers. ;

Mayra poured about 10 mL Of vinegar into a srnau plastic Cup. Then she recorded the initial temWature Of the vinegar as 22 •C. While the thermmleter was in the Cup, she added about teaspoon Of baking soda to the Cup. Mayra noticed the baking soda dissolved into the vinegar and bubbks started to form. She watched the thermometer for a change in temperature. After the fizzing stopped and the tenverature had stopped changing. Mayra recorded the final temperature as 15c

Which model most accurately represents the overall change that occurred in the cup

A) vinegar + baking soda— sodium acetate + carbon dioxide + water

B) vinegar + baking soda sodium acetate + carbon dioxide + water

C) vinegar + baking soda sodium acetate + carbon dioxide + water + energy

D) energy* vinegar + baking soda sodium acetate + carbon dioxide + water + energy

#### Groundwater Depletion

In many areas of the world, groundwater is being withdrawn from aquifers faster than natural recharge can replace it, this is called grwndwater overdraft

the extraction of groundwater can deplete this important. resource, but you know that overpumping welb cao also cause water quality issues

The quality, quantity, and reliability of groundwater resources are directly affected by the health of the aquifers

When wells are overdrawn, underlying salt water can rise into the wells and contaminate freshwater aquifers

From Reactants to Products

All synthetic materials are the result of chemical reactions. Substances react chemically in characteristic ways. You may recall that in a chemical reaction, the bonds between atoms in the reactants are broken. The atoms rearrange and make new bonds to form the products

The products have different properties than the reactants, the reactants underwent a chemical reaction called polymerization

Polymerization is the chemical process in which small organic molecules, or monomers, bond together to form a chain

A monomer is one of the small organic molecules that make up the long chain of a polymer Polymer chains can be very long

Polypropylene, which is used to make drinking straws, can have monomers in its chain

Natural Resource Availability

Natural resources are distributed unevenly around Earth

For example

iron ore is found near the surface of Earth and is mined easily in some regions in China. Large amounts of iron ore are used in the production of steel, a synthetic material, in other countries, iron ore is rare and steel must be imported, or brought into, the country

Climate also plays a role in natural resource availability —e One Of Russia's resources is timber, because its climate is favorable for growing large forests

Synthetic Material Production

In Russia, it is easy to make synthetic materials from timber because it is readily available The production and use of technology, such as synthetic materials, varies from region to region due to differences in climate and natural resource availability

Ecmomic cmditions Of a region also determine the production and uses Of synthetic materials. During favorable economic conditions, less effort is spent on synthetic materials that provide for basic living needs, because those needs are taken care of. More effort can be put into synthetic materials that improve a specific aspect of living, such as entertainment

#### Module: Matter; Properties and changes

Lesson 1: Properties of matter

Lab: Big enough https (/youtu.be/NydouLupr50

How can a substance's properties be measure"

Characteristics that you can observe (qualitative) or measure (quantitative) without changing the identity Of the matter are physical properties Of substances. These properties can be used to help identify a substance

1) Mass

Mass is the amount Of matter in a substance. If you pick up a small rock in one hand and a larger rock in the other hand, you can tell the larger rock is heavier and so it must have more mass. Because mass changes with the size of the object, mass is a size -dependent property

mass can be measured, so it is a quantitative property. Mass is measured in or grams (g). The instrument used to measure mass is called a balance. Types Of balances can include the following

Double pan balance

Triple beam balance

Mass is not the same as weight

Digital balance

Mass is the amount Of matter, or particles. in a Weight. measured by a scale, is the gravity on substance, but mass does not change with location

. Weight changes with location

If the objects were on the Moon, a balnce would read the same as it does here on Earth. A scale would give a different weight, because the pull of gravity is different on Earth than it is on the Moon