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4 years ago

The ___ numbers equals the _ of ____ electrons

Physics

1 answer:

suter [353]4 years ago

8 0

The atomic number equals the number of protons and electrons (in a neutral atom)

Explanation:

An atom is composed of three types of particles:

Protons: they are found in the nucleus of the atom. They are positively charged ( $q=+1.6\cdot 10^{-19}C$ ) and have a mass of approximately $m=1.67\cdot 10^{-27}kg$
Neutrons: they are also found in the nucleus. They have no electric charge and have a mass slightly larger than that of protons
Electrons: they orbit around the nucleus. They have negative electric charge ( $q=-1.6\cdot 10^{-19}C$ ) and are much lighter than protons, having a mass of $m=9.11\cdot 10^{-31} kg$ .

An atom is also identified by two numbers:

Atomic number (Z): it is equal to the number of protons in the nucleus
Mass number (A): it is equal to the number of protons+neutrons in the nucleus

For a neutral atom, the net electric charge is zero: this means that the number of protons equals the number of electrons. But since the number of protons corresponds to the atomic number Z, this means that the atomic number is also equal to the number of electrons, for a neutral atom.

Learn more about atoms:

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What is the melting point of substance A?

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Answer:

Solids are easily recognized by their ability to retain a fixed shape and definite volume. Particles making

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the solid does not have the ability to flow. (Although the particles of a solid do not move position to position, they do have motion in that they are constantly vibrating.

To change the temperature of a solid, heat energy must be added. The amount of heat energy that changes

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specific heat. The specific heat of ice is 2.1 Joules/g°C. In other words we must supply 1.0 gram of ice

with 2.1 Joules of heat energy to raise its temperature by 1.0 °C.

The general equation for calculating heat energy to change the temperature of a solid is:

Heat = Mass x Specific Heat (solid) x Temperature Change

Q = m c DT

10 g 10 g 10 g 10 g 10 g 10 g

Calculate the heat necessary to change 10 g of ice(s) at -20 °C to 10 g of ice(s) at 0°C. (A-B)

Q = mc∆T = (10 g) (2.1 J/g°C) (20°C) = 420 J

If you continue to add heat energy once the temperature of the ice reaches 0°C , the heat absorbed is called

the heat of fusion (Lf). This heat is used to cause a change of phase (from a solid to a liquid). This heat is

increasing the potential energy of the molecules of the solid. No temperature change takes place. Each

substance has its own heat of fusion. The heat of fusion for ice is 340 Joules/g. Exactly the same amount

of heat is given up when 1.0 g of water is changed to ice. This heat is called the heat of crystallization.

The general equation for calculating heat energy to change a solid to a liquid is:

Heat = Mass x Heat of Fusion

Q = m Lf

Calculate the heat necessary to change 10 g of ice(s) at 0°C to 10 g of water(l) at 0°C.(B-C)

Explanation:

Q = mLf = (10 g)( 340 J/g) = 3400 J

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3 years ago

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Answer:

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Explanation:

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3 years ago

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3 years ago

1.45 L of 16°C water is placed in a refrigerator. The refrigerator's motor must supply an extra 10.7 W power to chill the water

Vika [28.1K]

Answer:

The coefficient of performance of the refrigerator is 2.251.

Explanation:

In this case, the coefficient of performance of the refrigerator ( $COP$ ), no unit, is equal to the ratio of the heat rate received from the water to the power needed to work, that is:

$COP = \frac{\dot Q_{L}}{\dot W}$ (1)

$COP = \frac{\rho\cdot V\cdot c_{w}\cdot \Delta T}{\dot W \cdot \Delta t}$ (2)

Where:

$\dot Q_{L}$ - Heat rate received from the water, in watts.

$\dot W$ - Power, in watts.

$\rho$ - Density of water, in kilograms per cubic meter.

$V$ - Volume of water, in cubic meters.

$c_{w}$ - Specific heat of water, in joules per kilogram-degree Celsius.

$\Delta T$ - Temperature change, in degrees Celsius.

$\Delta t$ - Cooling time, in seconds.

If we know that $\rho = 1000\,\frac{kg}{m^{3}}$ , $V = 1.45\times 10^{-3}\,m^{3}$ , $c_{w} = 4187\,\frac{J}{kg\cdot ^{ \circ}C}$ , $\Delta T = 10\,^{\circ}C$ , $\dot W = 10.7\,W$ and $\Delta t = 2520\,s$ , then the coefficient of refrigeration of the refrigerator is: