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.