Thermochemistry

Thermochemistry The study of heat changes that occur during chemical reactions and physical changes of state

What is energy? Energy is the capacity to do work or to supply heat.

Kinds of Energy Potential energy- stored energy Kinetic energy- energy of motion Chemical potential energy- energy stored within the bonds of compounds. Radiant energy- energy from the sun

TPS- Classify the Type of Energy Wood Electric socket Moving baseball

What is the difference between Heat and Temperature? • Heat (q) energy transferred between samples because of differences in temperature. Depends on particle • speed • number • size • type of particles.

What is the difference between Heat and Temperature? • Temperature is a measure of the average kinetic energy of molecular motion in a substance. Temperature does not depend on the size or type of object.

Increasing/Decreasing Temp Adding Heat (energy) increases temperature and increases kinetic energy . Higher temperatures mean that the molecules are moving, vibrating and rotating with more energy. What would removing heat do???

Energy (Heat) Transfer • What happens if we bring two objects that are the same temperature in contact? • Now, what happens to the temperature if one object has a higher temperature than the other?

Law of Conservation of Energy In any chemical or physical process, energy is neither created nor destroyed. All energy can be accounted for as work, stored energy or heat.

Warm Up- Think about the types of energy(kinetic, potential and chemical potential. But it can change form Think of your own example and write it down!!

Measuring Heat- Important conversions Cal = (C) Food Calorie calorie = (cal) scientific calorie, amount of heat needed to raise 1g of water 1 degree C. Joule = (J) SI unit of heat and energy 1 Cal = 1000cal = 1kcal = 4186J 1J = 0.239 cal

Try these! • Express 60.1 cal in units of joules. 2. Express 975 J in cal and Cal.

Heat Capacity Amount of heat necessary to change an object’s temp. 1 degree.

Specific Heat Capacity (C) or (Cp) The amount of heat it takes to raise the temperature of 1g of the substance 1C. Helps you determine how much energy it takes to heat an known mass of a substance from one temperature to another. How much energy would it take to heat 50g of water from 50C to 100C?

Specific Heat Capacity (C) or (Cp) Water- 4.2 J/gC Alcohol- 2.4 J/gC Wood- 1.8 J/gC Aluminum- 0.90 J/gC Glass- 0.5 J/gC Check out the units! These are the key to upcoming problems

What do you remember about Direct and Indirect Proportions?

Two quantities are directly proportional if dividing one by the other gives a constant value. Y = k X What would the graph look like?

Two quantities are inversely proportional if their product gives a constant value. XY = K What would the graph look like?

Work on the POGIL Hoping you get this done in about 30 min…

Specific Heat Capacity q = m  t C q = energy (J) m = mass (g)  t = change in temperature (C)

Specific Heat Capacity q = m  t C q = energy (J) m = mass (g)  t = (Tfinal – T initial) = Change in temp

Doing specific heat problems • Write the equation q = m  t Cp • Manipulate equation to solve for the variable you want. • Plug the known values into the equation. Simple Huh?

During a phase change… There is no change in temperature… Q = mΔH ΔH(fus) = Heat of fusion ΔH(vap) = Heat of vaporization

Example Problem 1 • How much energy is required to raise the temperature of 15g of water from 25C to 75C? (The specific heat capacity of water is 4.18J/gC).

Practice 2- Do the problem and discuss the process with your partner. A particular sample of iron requires 562 J to raise it’s temperature from 35.0 °C to 70.0 °C. What is the mass of the sample? (Cp of iron is 0.449J/gC)

Problem 3 • If 100 J of heat energy is applied to 75g of mercury (Cp=0.140J/gC). How much will the temperature of mercury increase? • What is the final temperature if the initial temperature is 45 °C

Problem 4 Calculate the energy required to heat 25.0 g of aluminum (Cp=0.897J/gC) from 19.5 °C to 50.5 °C.

Warm Up You have 10 minutes to finish the POGIL and/or the Copper Lab calculations. Flip your POGIL to p.2 before turning it in. Paper Clip your lab teams packets togthr

Homework Any that you need me to look at with you?

Energy Values Really watch your changes in temperature because that determines the sign on q. +q = endothermic, absorbs energy -q = exothermic, releases energy

Energy in changes of state… Review the Freezing Point/Boiling Point graph from the beginning of the year.

What is happening with Energy When the graph is increasing temperature, kinetic energy is changing because the molecules are moving faster. When the graph plateaus, energy is still being absorbed, but it is being used to break intermolecular forces… potential energy is changing.

Remember…. The Processes EndothermicExothermic Δ H Vaporization = -Δ H Condensation Δ H Fusion = -Δ HSolidification

To Calculate the change in Energy… Use q = mΔtC for sections of the graph where kinetic energy changes. Use q = m ΔH (process) for sections of the graph

How can we measure the energy? Calorimeter- devices used to measure the amount of heat absorbed or released during a chemical or physical change

Important Vocabulary Terms System- specific area where you are focusing your attention Surroundings – everything outside the system

Thermochemistry