Matter and Energy

Drill

Define the following: State Process

Fill in the blanks: Specific enthalpy is an ______ property. If 2kg of water has a specific volume

of 0.3 m3/kg, it occupies _____ total space.

Matter and Energy

So far we have learned a bit about systems and how we describe them using properties.

Thermodynamics - study of systems and energy transfer

System – what we choose to study; can be open or closed

Boundary – separates system from surroundings

Surroundings – everything outside of system

Property – a characteristic used to describe a system• Extensive – “the whole is the sum of the parts,” Mass, Volume, Energy• Intensive – “the whole is the same as each part,” Density, Temperature

Now let’s learn how the state of a system can change through energy transfer.

Matter and Energy

So what is energy and how can it affect systems?

Thermodynamics - “the study of systems and energy transfer”

Piston & Cylinder

What do you think will happen to the system if we add weights to the top of the piston?What do you think will happen to the system if we lit a match underneath the cylinder?What would happen to the system if we placed the piston-cylinder in an ice bath?In each case, the system would change because of an energy transfer…

Matter and Energy

So what is energy and how can it affect systems?

Thermodynamics - “the study of systems and energy transfer”

Piston & Cylinder

Energy – the ability to do work or create heat

Energy In (Match)

Energy Out (Ice Bath)

Energy In (Weights)

Energy Transfer – occurs when energy moves in/out of a system

Matter and Energy

So now we know that energy can be either work or heat and can go in/out of a system…

Thermodynamics - “the study of systems and energy transfer”

Piston & Cylinder

…but what are work and heat, really?

Energy In (Match)

Energy Out (Ice Bath)

Energy In (Weights)

Matter and Energy

Work (W) = a force acting over some distance

Thermodynamics - “the study of systems and energy transfer”

If we pushed a block, we would be doing work on it…

Block

Mechanical Work = Force x Distance = F x d

Force

Distance Travelled

Matter and Energy

Work = a force acting over some distance

Thermodynamics - “the study of systems and energy transfer”

How much work is done on the block by a 5N force acting over 3 meters?

Block

Mechanical Work = Force x Distance = F x d

W = (5 N)(3 m) = 15 N-m = 15 J

Force

Distance Travelled

Matter and Energy

Mechanical work example:

Thermodynamics - “the study of systems and energy transfer”

Block

Mechanical Work = F x d

40 N

d = 3 m

W = (40 N)(3 m) W = 120 N-m

W = 120 J

Remember…only the component of the force that is parallel to the displacement does work.

Matter and Energy

Mechanical work example:

Thermodynamics - “the study of systems and energy transfer”

Block

Mechanical Work = F (cos)x d

40 N

d = 3

m

W = (40 N)(Cos 30O)(3 m) W = 103.9 N-m

W ≈ 104 J

Remember…only the component of the force that is parallel to the displacement does work.

30O

Matter and Energy

Heat (Q) – energy transfer caused by a temperature difference

Thermodynamics - “the study of systems and energy transfer”

If we place a flame beneath a system, we would be adding heat to it…we could also remove heat by surrounding the system with an ice bath.

Matter and Energy

Work and Heat can add/remove energy from a system, but what forms of energy do systems have?

Thermodynamics - “the study of systems and energy transfer”

Systems can have Potential Energy, Kinetic Energy, or Internal Energy.

Matter and Energy

Potential Energy (PE)Thermodynamics - “the study of systems and energy

transfer”

The block to the right will fall because a force equal to its mass times the acceleration of gravity is acting on it…

Block

PE = mghg = 9.8 m/s2

Height, h

Matter and Energy

Potential Energy Example:Thermodynamics - “the study of systems and energy

transfer”

BlockPE = mgh, where g = 9.8 m/s2

h = 3 m

m = 1.5 kg

PE = (1.5 kg)(9.8 m/s2)(3 m)PE = 44.1 kg-m2/s2

Remember, 1 N = kg-m/s2PE = 44.1 N-m

PE = 44.1 J

Matter and Energy

Kinetic Energy (KE)Thermodynamics - “the study of systems and energy

transfer”

If the block above moves with a velocity, V, then its kinetic energy is…

Block

2

2

1KE mV

Matter and Energy

Kinetic Energy Example:Thermodynamics - “the study of systems and energy

transfer”

If the block above moves with a velocity, V, then its kinetic energy is…

Block

Js

mkgsmkgKE 25)25)(2(

2

1)/5)(2(

2

12

22

m = 2 kgV = 5 m/s

2

2

1KE mV