7.3 Heat pp Mr. Richter

Agenda  Warm-Up  Check and Review HW  Business:  Collect/Return Lab Notebooks  Anyone who still owes me a quiz is taking it today after school!  Introduction to Heat  Notes:  Thermal Energy  Specific Heat Capacity  Calculating with Specific Heat Capacity  Lab Postponed Until Tomorrow

Objectives: We Will Be Able To…  Explain the difference between temperature and thermal energy.  Define heat.  Calculate the heat required to raise the temperature of a material.

Warm-Up:  Which do you think would be harder to melt: a 1 kg block of ice or a 1 kg block of iron? Why?  Discuss at your table. Then write a 1-2 sentence explanation in your notebook.

Thermal Energy What is heat?

Thermal Energy  Any object that has some temperature above absolute zero has some thermal energy, or energy due to its temperature.  The little vibrations of the atoms of that object have the ability to cause change.  The thermal energy of a hot stove can turn water into steam.  The thermal energy of the oceans can warm or cool an entire planet.

Thermal Energy  Thermal energy is the SUM of all of the random kinetic energies of the atoms or molecules of a substance.  Add up all of the kinetic energies of each individual atom.  Temperature is the AVERAGE of the random kinetic energies.  Do substances with the same temperature necessarily have the same thermal energy?  No! It depends on how much of each substances there is. More mass means more thermal energy!

Thermal Energy  What do we mean when we say “heat”?  When we say heat, we’re usually talking about something that  “feels warm”  “is hotter” than something else  We’re actually describing when thermal energy is flowing from one object to another. Heat flows naturally from hot objects (higher energy) to colder objects (lower energy).  Heat is just describing the transfer of thermal energy.

Specific Heat Capacity

 Does it take the same amount of energy to heat up a block of is as it does to heat up a block of iron?  Of course not! Every material has a different molecular structure.  This means that each material requires different amounts of energy to get its molecules or atoms to vibrate faster.

Specific Heat Capacity  Specific heat capacity is a measure of how much energy is required to raise the temperature of a substance.  Specifically (get it?), specific heat capacity is a measure of how much energy is required to raise the temperature of 1 kg of a substance by 1 °C.  For example:  the specific heat capacity (C) of water is 4,184  it takes 4,184 J to raise the temperature of 1 kg of water by 1°C.  this is approximately equivalent to 1 Calorie

Specific Heat Capacity  Some different specific heat capacities:  Which material requires more energy to raise its temperature by 10 °C: oil or silver?  Oil: its specific heat capacity is higher, so it requires more thermal energy to raise its temperature.

Calculating with Specific Heat Capacity

 The amount of energy required to change the temperature of an object depends on three things:  the specific heat capacity of the object (what material is it?)  the mass (how much?)  the change in temperature Q = mc Δ T Your BookMCAS

Calculating with Specific Heat Capacity  Use the chart on page How much energy is required to raise the temperature of 30 kg of steel from 15 °C to 30 °C? 2.How much energy is required to raise the temperature of 100 kg of water by 40 °C?

Wrap-Up: Did we meet our objectives?  Explain the difference between temperature and thermal energy.  Define heat.  Calculate the heat required to raise the temperature of a material.

Homework  Due Thursday  p. 179 #a, b  p. 180 # 1-3