Thermo chp 1, 2, 3

If a closed system consisting of a simple compressible substance is at equilibrium, only one phase can be present.

False

Carbon dioxide (CO2) at 320 K and 55 bar can be modeled as an ideal gas.

False P_C = 73.9 bar T_c = 304 K P_r = p/p_c =55/73.9 =0.7442 T_r = T/T_c =320/304 pr = 0.7442 Tr=1.0526 z = 0.75 not equal to 1 so carbon dioxide at this state cannot be modeled as an ideal gas

If superheated water vapor at 30 MPa is cooled at constant pressure, it will eventually become saturated vapor, and with sufficient additional cooling, condensation to saturated liquid will occur.

False at pressure 30 MPa, the critical pressure for water is p_c=220.9 bar (from the properties table), water cooling at constant pressure will never become a two-phase liquid-vapor mixture. since its above critical pressure

For a gas modeled as an ideal gas, C_v = C_p+R, where R is the gas constant for the gas.

False c_p - c_v = R c_p = c_v +R c_p and c_v are the specific heats and R is the gas constant c_v = c_p + R does not satisfies the ideal gas relation

Temperature is an extensive property.

False extensive properties depend on the size of the sys and temp does not depend

Mass is an intensive property.

False extensive properties depends on the size of the sys. it is the sum of values for the parts into which the sys is divided

For gases modeled as ideal gases, the ratio c_v/c_p must be greater than one.

False for an ideal gas c_p - c_v = R R is always positive its possible when c_v is less than 1 and c_p is greater than 1 therefore c_v<1 and c_p>1 (c_v/c_p) < 1

The specific internal energy of ammonia at 0.45 MPa and 50(Celsius) is 1564.32 kJ/kg.

False from superheated ammonia table p=0.45 MPa and T=50 Celsius which is inbetween 60 C and 40 C, therefore by interpolation between these temps to obtain the specific internal energy (u60-u40)/60-40 = (u60 - u50)/60-50 (1430.37-1393.80)/(60-40) = (1430.37-u50)/(60-50) u50=1412.085 kJ/kg

Kilogram, second, foot, and newton are all examples of SI units

False ft is english unit

A two-phase liquid-vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 0.5.

False generally vapor has a smaller density than quality x<.5

The composition of a closed system cannot change.

False in a closed sys, there is a transfer of energy but the quantity of matter remains constant

A control volume is a special type of closed system that does not interact in any way with its surroundings

False the control volume is separated from the surroundings by a control surface. Both mass and energy can enter or leave the control volume. The sys usually referred as open sys

If a closed system undergoes a process for which the change in total energy is positive, the heat transfer must be positive.

False whenever a closed sys undergoes a process, the term "heat transfer" may occur both into the sys and from the sys and a minimum negative value (heat transfer from the sys) of heat transfer may also correspond to a positive total energy change.

Air can always be regarded as a pure substance

False air is not a pure substance, bc air is composed of many different elements and compounds, like oxygen and nitrogen. Water is a pure substance

The total energy of a closed system can change as a result of energy transfer across the system boundary by heat and work and energy transfer accompanying mass flow across the boundary.

False bc a closed sys always contains the same substance or matter, energy can be transferred but there is no transfer of matter or substance across its boundaries to the surroundings therefore mass cannot flow through the boundary of a closed sys

If a closed system undergoes a thermodynamic cycle, there can be no net work or heat transfer.

False bc a closed sys can transfer energy with its surroundings through heat or work unter the thermodynamics cycle. In other words, work and heat are the forms that energy can be transferred across the boundary of the sys

The energy of an isolated system can only increase.

False bc an isolated sys is a special type of closed sys. There will be no interaction of mass or energy with the surroundings for example a thermoflask

A process that is adiabatic cannot involve work

False bc if a sys undergoes in an adiabatic process, no heat transfer can occur across the sys boundary, but work can be done in the sys

If a system's temperature increases, it must have experienced heat transfer.

False bc the temp of a sys may increase even by work transfer like stirring and heat transfer is not a prerequisite for increase in temp

For liquid water, the approximation v(T, p) ≈ v_f(T) is reasonable for many engineering applications.

True

Power is related mathematically to the amount of energy transfer by work by integrating over time.

True Power = work done / unit time power is the energy that is processed over a period of time

Atmospheric air is normally modeled as an ideal gas.

True atmospheric air is generally modeled as an ideal gas, bc its a mixture of several gasses present in the atmosphere. it is normally modeled as a uniform gas with the average properties from the individual components.

If a closed system undergoes a process for which the work is negative and the heat transfer is positive, the total energy of the system must increase.

True change in E = Q-(-W) so change in E = Q + W since the change in energy is positive the total energy of the sys increases

For simple compressible systems, any two intensive thermodynamic properties fix the state

True for simple compressible sys, the minimum required number of intensive thermo properties to fix an intensive state are two, like pressure and temp which are independent properties

Gage pressure indicates the difference between the absolute pressure of a system and the absolute pressure of the atmosphere existing outside the measuring device.

True gage pressure is the difference of absolute pressure and absolute atmospheric pressure measuring outside the device. The gage pressure always applied when the pressure of the sys more than the atmospheric pressure p(gage) = p(abs)-p_atm(abs)

If the value of any property of a system changes with time, that system cannot be at steady state.

True if a sys is said to be at steady state; none of its properties change with time, so if any property changes in the sys with time it cannot be at steady state

If a system is isolated from its surroundings and no changes occur in its observable properties, the system was in equilibrium at the moment it was isolated.

True if the sys is isolated from the surroundings -> if no changes occur in the sys then its in equilibrium at the moment it was isolated so the state is called equilibrium state

Temperature is the property that is the same for each of two systems when they are in thermal equilibrium

True if two sys are in thermal equilibrium, then they must have the same temp

The volume of a closed system can change.

True in a closed sys change in volume occurs; there is no transfer of matter or substance across its boundaries to the surroundings. if a piston moves in a cylinder, the work is done due to change in volume.

A closed system always contains the same matter; there is no transfer of matter across its boundary.

True in a closed sys energy can be transferred but the mass cannot be transferred across the boundaries to the surroundings

The properties of velocity and elevation are not included in the specification of an intensive thermodynamic state.

True in an intensive thermodynamic state, the properties of velocity and elevation are not included in the specifications bc they are independent properties. Only dependant variables like specific volume, enthalpy, entropy, internal energy are included in the tables.

Intensive properties may be functions of both position and time, whereas extensive properties can vary only with time

True intensive properties are independent on the size of the sys

When an ideal gas undergoes a polytropic process with n = 1, the gas temperature remains constant.

True pV^n =C P pressure, v is volume, and n is the polytropic index Theabove equation is generally useful for the compression and expansion proceses that include heat transfer if replace n with 1; the process is isothermal process. pv^1 = C pv=C

Pressure is an intensive property.

True pressure does not depend on the size of the sys so intensive

When a closed system undergoes a process between two specified states, the change in temperature between the end states is independent of details of the process.

True since the temp is a point func, the change in temp depends only on the end points of the process and its independent of the path of the process

The specific volume is the reciprocal of the density

True specific volume = volume / mass v = V/m =1/ (m/V) =1/p

Specific volume, the volume per unit of mass, is an intensive property whereas volume and mass are extensive properties

True specific volume is an intensive property bc it is independent on the amount of material, whereas mass and volume depends on the material so theyre extensive

The following assumptions apply for a substance modeled as an incompressible substance: The specific volume (and density) is constant and the specific internal energy is a function of temperature only.

True specific volume is constant and specific internal energy is a function of temp only

As pressure increases toward the critical pressure, the values of v_f and v_g approach each other.

True the change in specific volume from saturated liquid state to saturated vapor state increases as pressure decreases. Thus, if the pressure reaches critical pressure the saturated specific volume and superheated specific volume approach each other

The pressures listed in thermodynamic tables are absolute pressures, not gage pressures.

True the pressures listed in the thermodynamic tables are absolute pressures and not gauge pressures. The properties of the substance can be obtained at the absolute pressures not at gauge pressures.

Volume is an extensive property

True the volume depends on the size of the sys so extensive

A two-phase liquid-vapor mixture has 0.2 kg of saturated water vapor and 0.6 kg of saturated liquid. The quality is 0.25 (25%).

True x= m_vapor / (m_liquid + m_vapor) 0.2 kg for m_vapor and 0.6 kg for m_liquid x= 0.2 / (0.6+0.2) =0.25 =25%

A gas can be modeled as an ideal gas with constant specific heats when Z ≈ 1.

True yes gas can modeled as an ideal gas with constant specific heats at z=1

For heat pumps, the coefficient of performance lambda is always greater than or equal to one.

True bc The coefficient of performance for a heat pump can never be less than 1, it should always be greater than or equal to 1

For a system at steady state, no property values change with time.

True bc if a sys is said to be at steady state; none of its properties change with time. so, if any property changes in the sys with time, it cannot be at steady state

Only changes in the internal energy of a system between two states have significance: No significance can be attached to the internal energy at a state.

True bc if a sys undergoes a thermodynamic cycle, only changes in the energy of a sys have sig between states. There is no sig when the sys at a state

Thermal radiation can occur in vacuum.

True bc thermal radiation is one the modes of heat transfer. it can transfer heat without any medium. This is how we get energy from the sun. therefore thermal radiation can occur in vacuum

A spring is compressed adiabatically. Its internal energy increases.

True bc work is done on the sys by the surroundings to compress the spring adiabatically. The compressed spring has a greater capacity to do work. Therefore internal energy of the sys is increased by the amount of work done to it.

For any cycle, the net amounts of energy transfer by heat and work are equal.

True during in any thermodynamic cycle, the net amounts of energy transfer by heat and work are equal. there can be no net change in energy of a cycle

In principle, expansion or compression work can be evaluated using integrate p dV for both actual and quasiequilibrium expansion processes.

True p is the pressure and dV is the change in volume

Work is not a property.

True: work is not a property of the sys or the surroundings. work is a path variable and those are having inexact differentials

A polytropic process with n = k is adiabatic.

true