ENGR 112 Exam 2
Dimensional System
is defined as the smallest number of fundamental dimensions which form a consistent and complete set for a field of science. Example: Length - L Mass - M Time - T
Closed System
mass does not cross the boundaries of a closed system
Consumption
specifies an amount of an extensive quantity destroyed in a system during a specific time period
Generation
specifies an amount of an extensive quantity produced in a system during a time period
Input
specifies the amount of an extensive quantity added to the system during the time period.
Initial Amount
specifies the amount of an extensive quantity at the beginning of the time period
Final Amount
specifies the amount of an extensive quantity at the end of the time period
Output
specifies the amount of an extensive quantity leaving the system during the time period
Path Quantities
Are dependent on the path taken in a process
State Quantities
Are independent of the path a process takes
Explain dimensions and units and explain the difference between the two
Dimensions are used to describe physical quantities, e.g., length, time, mass, etc... Units describe the specific measure of a particular dimension, e.g. length -- meters, yards, cubits, etc... Dimensions are independent of Units
Universal Accounting Equation
Final amount - Initial amount = Input - Output + Generation - Consumption
Dimensional Homogeneity
For an equation to be valid, it must be dimensionally homogeneous The dimensions on the left-hand side must equal the dimensions on the right hand-side. F = ma
Open System
Mass crosses boundaries in an open system
Extensive Quantities
Quantities that do depend upon scale. Can be counted. Quantities that do change due to scaling. Examples: mass, moles, area, volume, energy, enthalpy
Intensive Quantities
Quantities that do not depend upon scale. Cannot be counted. Quantities that do not change due to scaling Examples: pressure, color, temperature, density
Consider driving from California to New York via North Dakota, Kansas, and Texas -What are some path quantities? -What are some state quantities?
State: Where you are and where you will be Path: Distance Traveled, Energy, Amount of Gas, Time, Number of stops, Food
A chemist performs a reaction in the laboratory and optimizes a reaction using the following conditions: T = 500 K P = 300 kPa Catalyst concentration = 50 g/L Catalyst amount = 25 g Reactor volume = 0.5 L Reactant amount = 300 g A chemical engineer is responsible for designing a plant that processes 50 tons per day of reactant. What quantities change, what quantities stay the same?
Stays Same: Temperature and Pressure Change: Everything Else.
Fundamental Dimensions
a dimension that can conveniently and usefully be manipulated when expressing all physical quantities of a particular field.
Derived Dimensions
a dimension that results from the combination of fundamental dimensions
Gravitational System of Dimensions
define force (F), length(L), and time (T). Mass (M) is a derived quantity, which is also determined from Newton's second law.
Absolute System of Dimensions
has dimensions that are not affected by gravity. L,T, and M are typical fundamental dimensions and Force(F) is a derived quantity determined from Newton's second law.