HVACR UNIT 7
The point at which water or another substance may exist simultaneously as a solid, liquid, and gas is:
Triple point.
The amount of space occupied by matter defines:
Volume
The substance that is used as the constant common material to measure specific gravity of solids is:
Water @ standard conditions.
A characteristic of water vapor, but not other states of water, is:
Water vapor is compressible.
Density is defined as
Weight divided by volume.
What is the relationship between atoms and molecules?
What is the relationship between atoms and molecules?
Changes in the volume of a gas can happen:
Whenever there is a change in temperature.
A container is half full of liquid. If the temperature of the liquid is increased, the liquid volume:
Will increase and the empty space remaining in the container will decrease.
Solids contain ________ amount of energy within materials or substances when they are in their various physical states.
the least
The AHRI definition of standard air is:
.075 lb/ft3 @ 70°F.
If a material or substance in the state of a liquid or solid has a specific gravity less than ________ it will float.
1.0
Standard atmospheric pressure is:
29.92 in Hg.
The temperature of the water formed by melting ice is:
32°F.
The wet bulb temperature for AHRI rating condition " A" is:
67°F.
The indoor dry bulb temperature for AHRI rating condition "A" is:
80°F.
What is the AHRI "A" performance testing condition for air-cooled air-conditioning equipment?
95°F outside ambient, 80°F indoor dry bulb, 67°F indoor wet bulb
Which of the following is accurate about gases?
A gas must be contained in a closed container or it will escape into the atmosphere.
The evaporation process occurs when:
A liquid is below its boiling point.
The definition of sublimation is:
A substance in a solid state changes into the gaseous state without going through the liquid state.
The ________ set of standard conditions are used to reference pressure and temperature when calculating specific gravity and specific volume of substances.
AHRI
The AHRI definition of standard air is:
Air weighing 0.075 lb/ft 3 at 70°F with a barometric pressure of 29.92 in Hg.
The substance used to compare the specific gravity of gases is:
Air.
A correct statement concerning inertia is:
All objects that are at rest have the tendency to stay at rest and when in motion tend to stay in motion.
When the performances of systems are analyzed, it is necessary to:
Analyze the systems under the same conditions to ensure an accurate analysis.
When a substance in the liquid state occupies a container, it:
Applies the greatest amount of pressure on the bottom of the container.
In contrast to liquids and vapors, solids will:
Apply downward pressure when set on a surface.
What is a practical use for knowing a substance's triple point?
Calibrating thermometers using the triple point temperature
The volume of a solid will:
Change very little when temperature changes occur.
What physical change of state is the opposite of evaporation?
Condensation
Which is occurring when gaseous molecules release heat and join together to form a liquid?
Condensing
The pressure and temperature at which there is no longer a difference between liquid and gas is called:
Critical point.
When a liquid-vapor mix is heated in a closed space, eventually the density of the liquid decreases and the density of the gas increases. When no difference between the liquid and vapor exists, it has reached its:
Critical point.
The density of a gas that occupies 30 cubic feet and weighs 3 pounds is:
Density = 3 lb/30 ft3 = 0.1 lb/ft 3.
A vapor that changes into a solid while bypassing the liquid state is known as:
Deposition.
The three states of matter represent:
Diverse levels of molecular energy within a material or substance.
In physics, solids and liquids:
Do not change in volume when pressures change, but gases will change.
Gravity causes liquids to exert force:
Downward and to the sides.
Gravity causes solids to exert force:
Downward.
Specific gravity is used in the HVACR industry:
For sizing gas lines.
Which of the following statements are TRUE for matter in a gas state?
Gas will exert equal pressure on all sides when inside a closed container.
Gravity causes gases to exert force:
In all directions.
How does pressure affect the boiling temperature of a liquid?
Increasing the pressure increases the boiling point.
How do industry organizations make it easier to compare testing results and rating for HVACR equipment?
Industry organizations determine a set of standard conditions that make all HVACR testing results comparable.
Natural gas floats on air. What does this tell us about its properties?
It has a lower specific gravity than air.
When a liquid boils:
It is absorbing heat while changing from liquid to gas.
If something has a high density:
Its specific volume is likely to be low.
Hot air is:
Less dense than warm air.
The triple point of most substances is:
Less than atmospheric pressure.
How does pressure affect boiling point?
Lower pressure decreases the boiling point of a substance
What is the difference between the weight and mass of an object?
Mass is not affected by gravity.
The law of conservation of matter states that:
Matter cannot be created or destroyed.
Elements are:
Naturally occurring chemicals.
If a gas with a specific gravity of 1.3 is released in a room, will it be more likely to be found near the ceiling or near the floor?
Near the floor because its specific gravity is greater than 1.
Evaporation occurs:
Only on the surface of a liquid.
Which units can be used to describe the density of a substance?
Pounds per cubic foot
The state in which a substance exists depends on:
Pressure and temperature.
If an HVACR technician determines the ratio of the density of a material to the density of a common material, what is she calculating?
Specific gravity
The specific volume of a gas that occupies 30 cubic feet and weighs 3 pounds is:
Specific volume = 30 ft3/3 lb = 10 ft3/lb.
Freezer burn occurs when water slowly exits perishable foods during the freezing process. This process is known as: (SERVICE TIP)
Sublimation
What physical change of state is the opposite of deposition?
Sublimation
How do environmental variables complicate HVACR testing?
Testing conditions, such as air pressure and temperature, can affect testing.
When sizing a compressor for a refrigeration application, the compressor is rated by: (TECH TIP)
The amount of refrigerant in cubic feet the compressor can move.
It is important to the HVACR technician to understand the changes of state of matter because:
The cooling and heating process requires a change of state of matter in some form.
Matter cannot be created or destroyed, but it can and does change form. This statement is known as:
The law of conservation of matter.
How would the law of conservation of matter explain what happens to a cup of water when it evaporates?
The liquid water is now water vapor of the same quantity.
The triple point of a substance is:
The point where a substance can exist as a solid, liquid, or vapor at the same time at one specific pressure and temperature.
When a vapor condenses:
The potential energy inside the molecules decreases.
Define critical point.
The pressure and temperature at which gas and liquid have the same properties
Define triple point
The pressure and temperature where a substance can exist simultaneously as a solid, a liquid, and a gas in thermal equilibrium
Specific gravity is defined as:
The ratio of the density of a material as compared to a common material.
Water will evaporate at a slower rate when:
The relative humidity is high
The calculations for density and specific gravity for Systems International (SI) are:
The same as AHRI standard conditions using metric values.
A molecule is:
The smallest part of a substance that is not an element.
Because liquids are noncompressible:
Their volumes will not change when pressures change.
