Chemistry Ms. Piela

 Heat transfers in chemical reactions  Energy  Definition: The capacity to do work or supply heat  Basic Types: Mechanical, Electrical, Potential, Kinetic

 Energy that is stored within chemical bonds  Determined by the arrangement and bonding of atoms  Examples: Gasoline, Food, etc

 Exothermic processes (‘exits’)  Heat flows out of a system

 System loses heat (negative sign)  Examples: Explosions!, Sun, Fire

 Endothermic processes (‘enter’)  Heat is absorbed from surroundings

 System gains heat (positive sign), Heat change is > 0  Examples: Boiling water, ice melting

 Energy transfers due to temperature differences between objects  Flows from hot to cold until temperature equilibrium is reached

 Energy cannot be created or destroyed, only transferred  Can be transformed  Example: HeatMechanicalElectrical

 Calorie (cal) – the amount of heat needed to raise 1 gram of water 1 ° C  Heat calorie is not to be confused with dietary calories  1 dietary Calorie = 1 kcal = 1000 cal  Joule (J) – metric unit of heat and energy Conversion Factor! Woo!

 It takes 50.2 J to raise the temperature of a g piece of glass. How many calories is this?

 A small chocolate bar has about 210,000 calories. How many Joules is this?

 The amount of heat required to raise 1 gram of a substance 1 ° C  Heat capacity is the amount of heat required to raise a substance 1 ° C

 q = heat (J or cal)  m = mass (g)  C = specific heat  ∆T = Change in Temp. ( °C)

 Specific heat plays a role in buffering climates  Specific heat of land = 0.8 J/g ° C  Specific heat of water = J/g ° C  How does this help buffer climates?  Water heats up slower and cools down slowly, releasing heat gradually

 On the notes, you’ll see a table of specific heat capacities for common metals.  We’ll be using these throughout all the problems in this section, so keep it handy!

 A 1.55 g piece of stainless steel absorbs 141 J of heat when its temperature increases by 178 ° C. What is the specific heat of stainless steel?.511 J/g ° C

 How much heat is required to raise the temperature of g of mercury from 52 ° C to 60 ° C? 280 J

 If the initial temperature of a 10.0 g substance is 20.0 ° C and J of heat are absorbed, what is the final temperature? The specific heat of the substance is 1.15 J/g ° C ° C