• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

1st law of thermodynamics

Extracts from this document...


1st law of thermodynamics

The first law of thermodynamics is shared with most of science; it is one of the fundamental principals that have shaped our understanding of the working world.

        TOTAL ENERGY OF THE SYSTEM AND IT’S SURROUNDINGS IS CONSTANT or ENERGY IS CONSERVED, Brings back that long established idea that nothing can be created or destroyed. How do we know this? This is an empirical law, which means that we know that energy is conserved because of many repeated experiments by scientists. It's been observed that you can't get any more energy out of a system than you put into it.

Latent heat

Latent Heat is defined as the heat which flows to or from a material without a change to temperature. The heat will only change the structure or phase of the material. E.g. melting or boiling of pure materials.

        One very good illustration of latent heat in action is observed when we reduce ice to water. If we imagine a bucket of ice on the floor in an average temperature room (about 30 degrees Celsius) .The ice doesn’t instantly liquidize, nor does the room instantly freeze. Instead the temperature of the ice rises until it reaches zero degrees Celsius whereupon it begins to melt.

...read more.


T= Temperature rise.


         Enthalpy is a measure of heat and energy in the system. Scientists figure out the mass of a substance when it is under a constant pressure. Once they figure out the mass, they measure the internal energy of the system. All together, that energy is the enthalpy. They use the formula "H = U + PV." H is the enthalpy value, U is the amount of internal energy, and P and V are Pressure and Volume of the system. This system works really well for gases.
        There are things that affect the level of enthalpy in a system. The enthalpy is directly proportional to the amount of substance you have. Chances are if you have more of a substance, you have more energy. More energy means higher enthalpy.
        Another thing to remember is that the value for H (enthalpy) changes sign when the reactions or values are reversed. When a reaction moves in one direction, the sign is positive. When a reaction is moves in the opposite direction, the value is negative.
        Finally we have Hess's law. If a process happens in stages or steps, then the enthalpic change for the overall system can be determined by adding the changes in enthalpy for each step.



...read more.


2) times the velocity of the water (cm / sec.) we get Cubic centimeters per second, volume per unit time, a rate of flow. It makes sense both ways. Does it matter what cross sections we use? If our principle that the quantity of matter flowing in, is the same as the amount flowing out then it must also be true everywhere in the pipe.

        Therefore we can say that  AV = K

Where A is cross sectional area at a point.

V is the average velocity for this point.

And K is a constant ‘the rate of flow in the pipe’.

Since the equation is true for any two points in the pipe we can say that :

A¹V¹ = A²V²

Where A¹V¹ is the area and velocity at one point in the pipe and A²V² is the area and velocity at another point.

This is called the continuity equation and it shows us that the velocity of water at a point in a full pipe is inversely proportional to the cross sectional area of the pipe  

at that point. So if a pipe gets bigger the velocity in the pipe will decrease and vice versa.


          Area at X is 10cm² and velocity is 1cm per second

        Area at Y is 1cm² and velocity is 10 cm per second


Stephen Amos HND Engineering YR1

...read more.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Electricity and Magnetism essays

  1. Rate of reaction

    makes them move around a lot more and collide more often with each particle colliding with enough energy to get it past the energy barrier. If this is done successfully, then the collisions should have no problem passing the requirement stated in the collision theory that are: To react particles

  2. Finding a material's specific heat capacity

    Then, some time after the heater has been switched off, the temperature will slowly fall. The temperature of the water is expected to rise more slowly and begin to cool much later. Also, by finding the energy transferred at any given time, the temperate can be plotted against the energy transferred for the linear section that rises linearly.

  1. charles law

    0.45 1.43 1.52 1.48 0.14 7.14 10 0.4 0.94 0.87 0.91 0.09 11.11 10 0.35 0.53 0.59 0.56 0.06 16.67 From table 1 you can see that when the length increases the periodic time increases therefore the frequency decreases.

  2. Ohms Law.

    * Do not switch on the power pack when there is no resistant wire and do not turn the power supply up too high because normal laboratory wires may melt Background knowledge Using a circuit such as this one on the left, an important general relationship can be seen.

  1. Investigating The Heat Of Combustion Of Alcohols.

    We waited till there was an increase of 20oC and then put the spirit burner out. The temperature was watched until it reached its peak and then noted down. The spirit burner was taken to the electric scales and weighed to see how much of its mass had been used up.

  2. Investigation in to what changes the temperature of a substance and how long this ...

    It is placed in through the cork lid. * Stop watch: This is used to count the amount of time the experiment has been running for. It will last for 5 minutes. Fair Test: These are the things that will make my experiment a fair one. * Use lagging to keep heat in.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work