Heat and Energy

What is the difference between temperature and heat?

What is the difference between temperature and heat? A measure of the random motions of the components of a substance The flow of energy due to a temperature difference Temperature Heat

Time = 0 Minutes 80°C Greater random motion 20°C Less random motion

Time = 20 Minutes 50°C 50°C Equivalent random motion

The Law of Conservation of Energy Energy can be converted from one form to another but can be neither created nor destroyed.

Exothermic Vs. Endothermic Greater random motion 20°C Less random motion Heat flow moves out of the system Heat flow moves into the system Exothermic Endothermic

Exothermic Vs. Endothermic Acetonitrile Methanol Water Water Heat flow moves out of the system Heat flow moves into the system Exothermic Endothermic

Endothermic Vs. Exothermic Reaction Graphs

Endothermic Vs. Exothermic Reaction Graphs Endothermic Reaction: a reaction in which the products have more stored energy than the reactants. The reaction ABSORBS energy from the surrounding environment and the products use up this energy to create chemical bonds. The products are colder than the reactants.

Endothermic Vs. Exothermic Reaction Graphs Exothermic Reaction: a reaction in which the products have less stored energy than the reactants. The reaction RELEASES energy when bonds are broken. The products are hotter than the reactants.

Exothermic Reaction Graph Total Potential Energy of the Activated Complex Activation Energy-the energy needed to start a reaction Energy stored in the Reactants E N R G Y Energy released in the reaction Energy Stored in the Products TIME

Endothermic Reaction Graph Energy of the Activated Complex Activation Energy-the energy needed to start a reaction Energy Stored in the Products Energy stored in the Reactants E N R G Y Energy absorbed in the reaction TIME

Specific heat capacity The amount of energy required to change the temperature of one gram of a substance by one Celsius degree. 1 g H2O Specific heat of water at 20̊ C = 4.184 J/g·Cº Specific heat of water at 20̊ C = 1.000 Cal/g·Cº

How do you convert Calories to Joules? 1 Cal = 4.184 J Express 95.1 Calories as Joules: 95.1 Cal X = 397.90 J = 400. J Please Note: The calories listed on food is actually KCal in the phys/chem world! 4.184 J 1 Cal

Calculating Energy Q = C X M X (Tfinal – Tinitial) or Q = C∙M ∙ ΔT Where q = energy (heat) required C = specific heat of material M = mass of the sample in grams ΔT is the change in temperature in Celsius degrees

Specific Heat Capacity* To Do Substance Specific Heat Capacity* Water (l) 4.184 Water (s) 2.03 Water (g) 2.0 Aluminum (s) 0.89 Iron (s) 0.45 Mercury (l) 0.14 Carbon (s) 0.71 Silver (s) 0.24 Gold (s) 0.13 Convert 34 calories to Joules A coke has 110 calories listed on the can (REMEMBER). Convert the value to Joules. How much heat (in calories) is needed to raise 20 grams of water from 5 °C to 40 °C? * Units are J / g °C

Specific Heat Capacity To Do 2 Substance Specific Heat Capacity Water (l) 4.184 Water (s) 2.03 Water (g) 2.0 Aluminum (s) 0.89 Iron (s) 0.45 Mercury (l) 0.14 Carbon (s) 0.71 Silver (s) 0.24 Gold (s) 0.13 How much heat (in calories) is needed to raise 140 grams of water from 20 °C to 25 °C? How many joules are needed to raise 50 grams of iron from 55 °C to 200 °C? A 2.6 g sample of metal requires 15.6 J of energy to change its temperature from 21°C to 34°C. Use reference info. to find this metal.

Practice A sample of gold requires 3.1 J to change its temperature from 19°C to 27°C. Is the metal pure gold? Determine the amount of energy as heat that is required to raise the temperature of a 10.0g sample of aluminum from 25°C to 58°C. Answer in Joules and calories If 294 J of heat is transferred to a 10.0 g sample of silver at 25°C, what is the final temperature of the silver? Okay, Achilles. If a 1.6 g sample of a metal that has the appearance of gold required 5.8J of energy to change its temperature from 23°C to 41°C. Is the metal pure gold? If you mix 25g of H20 at 84°C with 75g of water at 3°C, what will the final temperature of the water be?

Quick Quiz What is the difference between temperature and heat? You mix methanol and water, and the temperature of the mixture increases to 70°C. Is the reaction endothermic or exothermic? The specific heat for air is 1.012 J/g C°. The specific heat for carbon dioxide is 5.0 J/g C°. Explain why increased concentrations of carbon dioxide could be dangerous to Earth dwellers. What is the difference between calories listed on a box of Oreos and calories as defined by scientists? You are testing Oreo Cakesters. The box label states that 1 serving = 250 cal. If one serving is 57g and the change in temperature is from 23°C to 42°C, What is the specific heat capacity? Be careful about what is underlined!