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two metal blocks that have slightly different temperatures are placed next to one another. after five minutes, they both have lower but equal temperatures. according to the law of conservation of energy, what most likely happened?

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get two metal blocks that have slightly different temperatures are placed next to one another. after five minutes, they both have lower but equal temperatures. according to the law of conservation of energy, what most likely happened? from EN Bilgi.

Thermodynamics

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Law of Thermodynamics

Thermodynamics is a very important branch of both physics and chemistry. It deals with the study of energy, the conversion of energy between different forms and the ability of energy to do work. As you go through this article, I am pretty sure that you will begin to appreciate the importance of thermodynamics and you will start noticing how laws of thermodynamics operate in your daily lives! There are essentially four laws of thermodynamics.

Zeroth Law of Thermodynamics

“If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with one another”

Let’s first define what ‘thermal equilibrium’ is. When two systems are in contact with each other and no energy flow takes place between them, then the two systems are said to be in thermal equilibrium with each other. In simple words, thermal equilibrium means that the two systems are at the same temperature. Thermal equilibrium is a concept that is so integral to our daily lives. For instance, let's say you have a bowl of hot soup and you put it in the freezer. What will happen to the soup? The soup will, of course, start cooling down with time. You all know that. And you also probably know that the soup will continue to cool down until it reaches the same temperature as the freezer. Even if you are familiar with this concept, what you may not realize is that this is an excellent example of thermal equilibrium. Here, heat flows from the system at a higher temperature (bowl of soup) to the system at a lower temperature (freezer). Heat flow stops when the two systems reach the same temperature. In other words, now the two systems are in thermal equilibrium with each other and there is no more heat flow taking place between the two systems. Let’s assume we have three systems - system 1, system 2 and system 3. Their temperatures are T

_1 1 ​

start subscript, 1, end subscript

, T _2 2 ​

start subscript, 2, end subscript

and T _3 3 ​

start subscript, 3, end subscript

respectively.

Diagram showing the zeroth law

The Zeroth law states that if the temperature of system 1 is equal to temperature of system 3, and the temperature of system 2 is equal to temperature of system 3; then the temperature of system 1 should be equal to the temperature of system 2. The three systems are said to be in thermal equilibrium with each other.

That is; if T _1 1 ​

start subscript, 1, end subscript

= T _3 3 ​

start subscript, 3, end subscript

and T _2 2 ​

start subscript, 2, end subscript

= T _3 3 ​

start subscript, 3, end subscript

, then T _1 1 ​

start subscript, 1, end subscript

= T _2 2 ​

start subscript, 2, end subscript

The zeroth law is analogous to the basic rule in algebra, if A=C and B=C, then A=B.

This law points to a very important fact - ‘temperature affects the direction of heat flow between systems.’ Heat always flows from high temperature to low temperature. Heat flow is mathematically denoted as ‘Q’.

First Law of Thermodynamics

This law is essentially the ‘law of conservation of energy’. Energy can neither be created nor destroyed; it can just be converted from one form to another.

In simple words, the first law of thermodynamics states that whenever heat energy is added to a system from outside, some of that energy stays in the system and the rest gets consumed in the form of work. Energy that stays in the system increases the internal energy of the system. This internal energy of the system can be manifested in various different forms – kinetic energy of molecules, potential energy of molecules or heat energy (that simply raises the temperature of the system).

What is internal energy?

It is defined as the sum total of kinetic energy, which comes from motion of the molecules, and potential energy which comes from the chemical bonds that exist between the atoms and any other intermolecular forces that may be present.

First law of thermodynamics is thus conventionally stated as: “The change in internal energy of a closed system is equal to the energy added to it in the form of heat (Q) plus the work (W) done on the system by the surroundings.”

Mathematically, this can be put as

∆E _{internal} internal ​

start subscript, i, n, t, e, r, n, a, l, end subscript

= Q + W

Conventional definition of the first law is based on the system gaining heat and the surrounding doing work. The opposite scenario can occur too, in which case the ‘signs’ in the equation will have to be changed appropriately. This will be discussed shortly.

Lots of times you will notice that ∆E

_{internal} internal ​

start subscript, i, n, t, e, r, n, a, l, end subscript

is also denoted as ∆U.

Now you must be wondering what is meant by a ‘closed system’. Let’s try to understand this through a simple example. Imagine we have two saucepans containing water - 1) with a lid 2) without a lid. Both are kept on a heated stove.

Backpacker

Backpacker brings the outdoors straight to the reader's doorstep, inspiring and enabling them to go more places and enjoy nature more often. The authority on active adventure, Backpacker is the world's first GPS-enabled magazine, and the only magazine whose editors personally test the hiking trails, camping gear, and survival tips they publish. Backpacker's Editors' Choice Awards, an industry honor recognizing design, feature and product innovation, has become the gold standard against which all other outdoor-industry awards are measured.

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Backpacker brings the outdoors straight to the reader's doorstep, inspiring and enabling them to go more places and enjoy nature more often. The authority on active adventure, Backpacker is the world's first GPS-enabled magazine, and the only magazine whose editors personally test the hiking trails, camping gear, and survival tips they publish. Backpacker's Editors' Choice Awards, an industry honor recognizing design, feature and product innovation, has become the gold standard against which all other outdoor-industry awards are measured.

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Physics

11.2 Heat, Specific Heat, and Heat Transfer

11.2 Heat, Specific Heat, and Heat Transfer

SECTION LEARNING OBJECTIVES

By the end of this section, you will be able to do the following:

Explain heat, heat capacity, and specific heat

Distinguish between conduction, convection, and radiation

Solve problems involving specific heat and heat transfer

Section Key Terms

conduction convection heat capacity radiation specific heat

Heat Transfer, Specific Heat, and Heat Capacity

We learned in the previous section that temperature is proportional to the average kinetic energy of atoms and molecules in a substance, and that the average internal kinetic energy of a substance is higher when the substance’s temperature is higher.

If two objects at different temperatures are brought in contact with each other, energy is transferred from the hotter object (that is, the object with the greater temperature) to the colder (lower temperature) object, until both objects are at the same temperature. There is no net heat transfer once the temperatures are equal because the amount of heat transferred from one object to the other is the same as the amount of heat returned. One of the major effects of heat transfer is temperature change: Heating increases the temperature while cooling decreases it. Experiments show that the heat transferred to or from a substance depends on three factors—the change in the substance’s temperature, the mass of the substance, and certain physical properties related to the phase of the substance.

The equation for heat transfer Q is

Q = mcΔT, Q = mcΔT, 11.7

where m is the mass of the substance and ΔT is the change in its temperature, in units of Celsius or Kelvin. The symbol c stands for specific heat, and depends on the material and phase. The specific heat is the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00 ºC. The specific heat c is a property of the substance; its SI unit is J/(kg

⋅ ⋅ K) or J/(kg ⋅ ⋅ °C °C

). The temperature change (

ΔT ΔT

) is the same in units of kelvins and degrees Celsius (but not degrees Fahrenheit). Specific heat is closely related to the concept of heat capacity. Heat capacity is the amount of heat necessary to change the temperature of a substance by 1.00

°C °C

. In equation form, heat capacity C is

C=mc C=mc

, where m is mass and c is specific heat. Note that heat capacity is the same as specific heat, but without any dependence on mass. Consequently, two objects made up of the same material but with different masses will have different heat capacities. This is because the heat capacity is a property of an object, but specific heat is a property of any object made of the same material.

Values of specific heat must be looked up in tables, because there is no simple way to calculate them. Table 11.2 gives the values of specific heat for a few substances as a handy reference. We see from this table that the specific heat of water is five times that of glass, which means that it takes five times as much heat to raise the temperature of 1 kg of water than to raise the temperature of 1 kg of glass by the same number of degrees.

Substances Specific Heat (c)

Solids J/(kg ⋅°C ⋅°C ) Aluminum 900 Asbestos 800

Concrete, granite (average) 840

Copper 387 Glass 840 Gold 129

Human body (average) 3500

Ice (average) 2090 Iron, steel 452 Lead 128 Silver 235 Wood 1700 Liquids Benzene 1740 Ethanol 2450 Glycerin 2410 Mercury 139 Water 4186

Gases (at 1 atm constant pressure)

Air (dry) 1015 Ammonia 2190 Carbon dioxide 833 Nitrogen 1040 Oxygen 913 Steam 2020

Table 11.2 Specific Heats of Various Substances.

Temperature Change of Land and Water

What heats faster, land or water? You will answer this question by taking measurements to study differences in specific heat capacity.

Open flame—Tie back all loose hair and clothing before igniting an open flame. Follow all of your teacher's instructions on how to ignite the flame. Never leave an open flame unattended. Know the location of fire safety equipment in the laboratory.

Sand or soil Water Oven or heat lamp Two small jars Two thermometers Instructions Procedure

Place equal masses of dry sand (or soil) and water at the same temperature into two small jars. (The average density of soil or sand is about 1.6 times that of water, so you can get equal masses by using 50 percent more water by volume.)

Heat both substances (using an oven or a heat lamp) for the same amount of time.

Record the final temperatures of the two masses.

Now bring both jars to the same temperature by heating for a longer period of time.

Remove the jars from the heat source and measure their temperature every 5 minutes for about 30 minutes.

Soil has an approximate specific heat of 800 J / kg °C. A farmer monitors both the soil temperature of his field and the temperature of a nearby pond as winter sets in. Will the field or the pond reach 0 °C first and why?

The pond will reach 0 °C first because of water’s greater specific heat.

Source : openstax.org

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James 16 day ago

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