Matter and Energy

Drill Identify which of the two descriptions of your class is an intensive property and which is extensive: The number of students in the class. The grade level of the students in class.

Thermodynamics - study of systems and energy transfer Matter and Energy This course is an introduction to the study of thermodynamics and an investigation of how it can be applied to renewable and non- renewable energy sources. Thermodynamics - study of systems and energy transfer System – what we choose to study Boundary – separates system from surroundings Surroundings – everything outside of system

Thermodynamics - “the study of systems and energy transfer” Matter and Energy Thermodynamics - “the study of systems and energy transfer” There are two types of systems… Closed Systems – no mass crosses the boundary Open Systems – mass crosses the boundary “Energy can cross the boundary of both open and closed systems.” Energy in… Energy out…

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system There are two types of properties: 1) Extensive – the whole equals the sum of its parts 2) Intensive – the whole is the same as any part EXTENSIVE INTENSIVE Mass Volume Temperature Pressure Mass, Temperature and Pressure are exceptions to the rule: Mass (m) is extensive; Temperature (T) and Pressure (P) are intensive. Extensive properties usually use capital letters as symbols. Extensive properties usually use lower case letters as symbols. Mass and Volume are both extensive properties. Temperature and Pressure are intensive properties.

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system Property Symbol Definition Mass m measure of the amount of material present Volume V amount of space occupied by an object Energy E the ability to do work or produce heat Temperature T measure of the molecular activity of a substance Pressure P force exerted per unit area on the boundaries of a substance Density ρ the total mass of a substance divided by the total volume What type of property is density, ρ? What type of property is energy, E? Intensive Extensive

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system In general, an extensive property can be made intensive by dividing by the mass of the system. Extensive Divide by Mass Intensive Energy E kilojoules, kJ Energy/mass E/m kilojoules/kilogram Specific Energy e kJ/kg When an extensive property is made intensive by dividing by mass, we use a lowercase symbol and the prefix “specific”.

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system Let’s work an example: A closed steel tank contains 3 kg of water in the form of vapor and liquid. The volume of the tank is 18 m3. Calculate the specific volume of the water in the tank:

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system A closed steel tank contains 3 kg of water in the form of vapor and liquid. The specific energy of the water in the tank is 126 kJ/kg. Calculate the total energy of the water in the tank:

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system There are two types of properties: State – a list of all the property values of a system 1) Extensive – the whole equals the sum of its parts 2) Intensive – the whole is the same as any part To truly describe a system, you must be able to list all of the properties of that system…you must know the state of that system. We now know that properties help to describe systems, that there are extensive and intensive properties, and how to convert from intensive to extensive and vice versa. But properties can change over time; when any property changes, the state of the system also changes.

Property – a characteristic used to describe a system Matter and Energy Property – a characteristic used to describe a system State – a list of all the property values of a system A snapshot of the dashboard of a car would tell you the state of the car at that point in time. ...the oil pressure climbs (pressure), etc. In short, the state of your car changes as you speed up and slow down. If someone took pictures as you drove, they would capture a record of a series of states for your car. That record of states is a process. You can think of the state of the system as a snapshot, a picture, of all of the property values of a system at some point in time. Let’s say you take your car out for a drive. As you drive, you burn fuel (lose mass), your engine heats up(temperature)… Process– a record of all the states that a system passes through 1 2 3 4 5 6 Pressure Energy State Mass Temperature Process