Physics Chapter 10 Test

A volume of cool air rapidly descends from the top of a mountain. The air is a poor thermal conductor, but its temperature increases as its volume decreases, because of the increase in atmospheric pressure as it reaches the ground. What thermodynamic process takes place? (Ask Mrs Hopper in Morning)

Adiabatic

Explain how energy can be transferred as heat and work in an isothermal process and yet the internal energy of the system remains unchanged.

For an isothermal system, Delta U is 0, Delta T = 0, so Q = W

When gas compresses, the work done on the gas is what...?

Negative

Is it possible to construct a heat engine that doesn't transfer energy to its surroundings? Explain. (Ask Mrs Hopper if it is greater than zero)

No, because energy removed as heat (Qc) can never equal zero.

What is efficiency measured in?

Nothing, it is a unitless quantity

When gas expands, the work done by the gas is what...?

Positive

What are the characteristics of the compressor?

Q = 0, W is negative, ∆U is positive

What are the characteristics of the expansion valve?

Q = 0, W is positive, and ∆U is negative

What are the characteristics of the condenser?

Q is negative, W = 0, ∆U is negative

What are the characteristics of the evaporator?

Q is positive, W = 0, and ∆U is positive

Use the first law of thermodynamics to show that the internal energy of an isolated system is always conserved. (Ask Mrs Hopper is answer is right)

The 1st law of thermodynamics states that energy can be neither created nor destroyed; it can only change forms. In any process within an isolated system, the internal energy remains constant.

What is true about ideal cyclic processes?

The net work done equals the net transfer of energy as heat.

Explain why opening the refrigerator door on a hot day does not cause your kitchen to become cooler.

The thermodynamic process that releases energy out to the room around it. This means that there will be no drop in temperature.

Explain how a cyclic process resembles and differs from an isothermal thermodynamic process.

They are the same because internal energy equals zero in both and temperature always returns to its original state

What is the equation for Work?

W = P∆V

What is an example of a natural process that has involves a decrease in entropy? What is the corresponding entropy increases in the environment?

When water freezes in winter, the energy transferred from water to air increases the air's entropy.

Efficiency

a measure of how well an engine operates

Adiabatic Process

a rapid thermodynamic process during which no energy is transferred to or from the system as heat

System

a set of particles or interacting components considered to be a distinct physical entity for the purpose of study.

Cyclic Process

a thermodynamic process in which a system returns to the same conditions under which it started

Isothermal Process

a thermodynamic process that takes place at constant temperature

Isovolumetric Process

a thermodynamic process that takes place at constant volume so that no work is done on or by the system

Heat Engine

an engine that uses heat to do mechanical work

Use the second law of thermodynamics to explain why a heat engine cannot be 100 percent efficient.

because energy added as heat is always greater than energy removed as heat

Which concept does the first law of thermodynamics describe?

conservation of energy

What is the efficiency equation?

eff = 1 - Qc/Qh

What happens to a system when Q > 0?

energy is added to the system as heat

What happens to a system when Q < 0?

energy is removed from the system as heat

What are the 4 steps of the refrigerator?

evaporator, compressor, condenser, expansion valve

No work is done on or by a system when...?

gas volume remains constant

The more disorder, the ______ the entropy.

greater

What are two examples of cyclic processes?

heat engines and refrigerators

What are the 4 steps of an engine?

intake, compression, combustion, exhaust

The 2nd Law of Thermodynamics states...? (Give it's definition)

no cyclic process that converts heat into work is possible

What happens to a system when Q = 0?

no transfer of energy as heat is done

What happens to a system when W = 0?

no work is done

Environment

the combination of conditions and influences outside a system that affect the behavior of the system

According to the second law of thermodynamics, work (W) can never equal what...?

the energy added as heat (Qh)

Express the 2nd Law of Thermodynamics in terms of entropy change.

the entropy of the universe increases in all natural processes

Internal-Combustion Engine

the heat engine found in most vehicles

Entropy

the measure of a system's disorder or randomness

1st Law of Thermodynamics

the principle of energy conservation that takes into account a system's internal energy as well as work and heat

What are conditions for an isothermal process?

there is no change in temperature and internal energy

What are conditions for an adiabatic process?

there is no energy transferred as heat

What are conditions for an isolated system?

there is no heat or work interaction with surroundings

What are conditions for an isovolumetric process?

there is no work done

Work is only done if...?

volume changes

When is mechanical energy not conserved?

when friction is taken into account

What happens to a system when W > 0?

work is done by the system (expansion of gas)

What happens to a system when W < 0?

work is done on the system (compression of gas)

What is the change of internal energy for cyclic processes?

zero

What is the 1st Law of Thermodynamics expressed mathematically?

∆U = Q - W