Heat & Temperature

Internal Energy Internal Energy Consider the energy of an object. How can you change the energy of an object? e.g. you.

Internal Energy Internal Energy The internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms of molecules.

Heat & Temperature Heat Vs Temperature What is the difference between heat and temperature? Which is hotter –a candle flame or a bath of hot water?

Heat & Temperature Heat Vs Temperature Heat is a type of energy, measured in Joules (J). It is the sum of the kinetic energies of all the particles. Temperature is a measure of the average kinetic energy of the particles. The faster they move, the higher the temperature. In other words, how ‘hot’ it is.

Heating an object Heat Vs Temperature Explain what happens to the temperature of an object and hence its internal energy when it is heated.

What happens to particles in an object if you heat it? Heat Vs Temperature The particles move faster, pushing further apart. This means the whole object expands. Eventually it will change state. e.g. Solid to liquid. THE PARTICLES THEMSELVES DO NOT EXPAND!

Measuring Temperature Heat Vs Temperature We use the property of expansion on heating to measure temperature. What usually expands inside a thermometer?

Temperature In the 19th century the concept of temperature was related to the random motion of particles. It has been found that there is a direct relationship between temperature and the average random kinetic energy using the Kelvin scale. At absolute zero (0 K) the kinetic energy of particles = 0 Kinetic energy (1/2 m v ^2) /J Temperature / K

Temperature scales Brain use time: The temperature of the body increases from 320 K to 340 K. State the temperature increase in degrees C. It’s supposed to reach 8 degrees C today, what is that in Kelvin? 20 ⁰C 281 K

Measuring temperature Temperature can be measured by any device where on property changes with a predictable way as temperature changes (Thermionic device). E.g. in a liquid – in- glass thermometer the liquid expands by a fixed amount as it is heated. In a digital thermometer a thermistor is used, where the resistance of the metal varies with temperature.

Thermal Equilibrium The condition under which two substances in physical contact with each other exchange no heat energy. Two substances in thermal equilibrium are said to be at the same temperature. Substances in contact with each other will undergo a thermal interaction, whereupon energy is transferred until both bodies are at the same temperature. The object with highest energy (the hotter object) will always transfer energy to the object with lower energy (the cooler object). The total energy of the system remains constant. The rate of transfer depends on the conductivity of the objects

Heat Heat is the energy that is transferred from one body to another as a result of difference in temperature. Heat was once thought to be a fluid (called Caloric) that moved from body to body. The more caloric a body contained the hotter it was, and as caloric left the body it became colder. This idea was rejected when people realised that you could warm your hands by rubbing them together. If caloric entered your hands then another body must become colder, and this is not true. In the 19th century heat was shown to be another form of energy.

Rate my thermometer A B C D E F G H

Rate my thermometer Use your knowledge of heat (and how materials behave when heated) to decide on which design of thermometer is best. You must be able to justify why you have chose one design over another

The winner is….. D Thin walls for the bulb Thick walls for the stem Allows easy conduction so the liquid inside is heated quickly and easily Thick walls for the stem Protection for the thin tube inside Thin capillary tube inside Higher sensitivity (a small expansion will produce a large change in height) Small volume of liquid in bulb Less energy is required to heat the liquid so it’s temperature will change more easily making it more responsive

NEXT LESSON……you will be carrying out a super easy but important practical You will be provided with: 250 mL Beakers Water Thermometer Stopwatch Hotplate

What are you going to do? Fill a beaker with 100 mL of water and measure its starting temperature Place the beaker on your hotplate and start the stopwatch at the same time Heat for a set amount of time (e.g. 3 min), recording the temperature every 30 seconds Repeat practical using 200 mL of water in a fresh beaker ***DO NOT TOUCH THE BEAKER ONCE IT HAS BEEN OVER THE HOTPLATE***

What you need to do now: Prediction – what do you think will happen? Will one beaker have a higher temperature than the other at the end or will they be at the same temperature? If they are different temperatures which will be higher? Procedure – give a step-by-step explanation (bullet pointed) of how you will carry out the practical. Explain what measurements you will make Diagram – Draw a labelled diagram of the set-up Results – Draw a results table using a ruler and pencil. Ensure that your units are in the headings

Health and Safety THE USUAL – when instructed, place all books, planners, etc on your stool and push your stool and bag under the desk GLASS – Please place all equipment in the centre of the desk to avoid knocking it over. If you do break something, inform me immediately. HOT WATER + GLASS – You are to be standing at ALL times in order to be able to move out of the way quickly if water is spilt. DO NOT TOUCH HOT GLASS. Inform me when you are done collecting results for each beaker and I will remove it. HOT POTATO – The hotplate will be hot at the end. Do not touch or move it.

And now…. Graph – plot a graph of temperature vs time (time on x-axis). You will have 2 trend lines…one for 100 mL and one for 200 mL Conclusion – What do your results tell you? Do they agree with your prediction? Can you explain the results in scientific terms? Evaluation – What did you do well in your experiment? Do you think your results are reliable? Why or why not? How could your experimental method be improved if you were to do the practical again?