Thermochemistry Intro

​Thermochemistry

Many chemical reactions occur within your body when you exercise. As these reactions take place, your body gets hot and you sweat. What about these reactions causes such a drastic change in your body?

Introduction

• Virtually every chemical reaction is accompanied by a change in energy

• Thermochemistry: the study of the transfers of energy as heat that accompany chemical reactions and physical changes​

Collisions in Reactions

• Reactions happen when bonds are broken and atoms of reactants are rearranged

  • Collision Theory: Bonds are broken and/or formed when reactant particles collide with enough energy and the correct orientation​

The Activated Complex

• The Activated Complex: an unstable cluster of atoms that exist during the transition between reactants and products

Systems and Surroundings

• System: the specific part of the universe that a scientist studies

  • Everything outside of the system is the surroundings

  • Energy can transfer between a system and the surroundings

Investigation 8 | Experience 1

Temperature

• Temperature: the measure of the average kinetic energy of the particles in a sample of matter

  • The greater the kinetic energy, the higher the temperature and the hotter it feels

  • SI Unit for Temperature is Kelvin

    • °C +273

Investigation 8 | Experience 1

Heat

• Heat: The energy transferred from one object to another due to a temperature difference

  • Happens through radiation or the collision of particles

  • This will happen until a balance is reached and both objects are at the same temperature

  • Heat always flows from warmer objects to cooler objects

  • Measured in a chemical reaction with a calorimeter

  • SI Unit of heat and other forms of energy is the joule

Investigation 8 | Experience 1

Heat

Investigation 8 | Experience 1

Specific Heat

• Different metals have differing capacities to absorb and release energy

  • A method to compare these capacities is necessary

• Specific Heat: the amount of energy required to raise the temperature of one gram of a substance by 1 °C or 1 kelvin

  • usually measured under constant pressure and shown by the symbol c_p

  • matter with a high specific heat needs more energy to raise the temperature

Investigation 8 | Experience 1

Specific Heat formula

Investigation 8 | Experience 1

Specific Heat Sample Problem 1

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • What is the specific heat of this type of glass?

  • How much energy will the same glass sample gain when it is heated from 314 K to 344 K

• Step 1: Identify what variables we know

  1. c_p

  2. m

  3. Δ​T

  4. q

Investigation 8 | Experience 1

Specific Heat Sample Problem 1

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • What is the specific heat of this type of glass?

  • How much energy will the same glass sample gain when it is heated from 314 K to 344 K

• Step 1: Identify what variables we know

  1. c_p=?

  2. m=4.0 g

  3. Δ​T= 314-274 = 40 K

  4. q=32 J

Investigation 8 | Experience 1

Specific Heat Sample Problem 1 a

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • What is the specific heat of this type of glass?

• Step 2: Find the specific heat by plugging into the specific heat equation

Investigation 8 | Experience 1

Specific Heat Sample Problem 1 b

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • How much energy will the same glass sample gain when it is heated from 314 K to 344 K

• Step 3: Identify the variables we know

  • c_p=

  • q=

  • m=

  • ΔT=

Investigation 8 | Experience 1

Specific Heat Sample Problem 1 b

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • How much energy will the same glass sample gain when it is heated from 314 K to 344 K

• Step 3: Identify the variables we know

  • c_p= 0.20J​

  • q=?

  • m=4.0

  • ΔT=344-314=30

Investigation 8 | Experience 1

Specific heat Sample Problem 1 b

• A 4.0 gram sample of glass was heated from 274 K to 314 K and was found to have absorbed 32J of energy as heat

  • How much energy will the same glass sample gain when it is heated from 314 K to 344 K

• Step 4: Plug our Variables into our energy equation

Investigation 8 | Experience 1

Specific heat Sample Problem 2

• Determine the specific heat of a material if a 35 g sample absorbed 48 J as it was heated from 293 K to 313 K

  • Step 1: Identify what variables we know

    1. c_p

    2. m

    3. Δ​T

    4. q

Investigation 8 | Experience 1

Specific heat Sample Problem 2

Investigation 8 | Experience 1

Specific heat Sample Problem 3a

• A 85 g piece of Copper Alloy is heated from 30 °C to 45°C. In the process it absorbs 523 J of energy as heat. What is the specific heat of this copper alloy?

  • Step 1: Identify what variables we know

    1. c_p

    2. m

    3. Δ​T

    4. q

Investigation 8 | Experience 1

Specific heat Sample Problem 3a

• A 85 g piece of Copper Alloy is heated from 30 °C to 45°C. In the process it absorbs 523 J of energy as heat. What is the specific heat of this copper alloy?

  • Step 1: Identify what variables we know

    • c_p=?

    • m= 85

    • Δ​T= 45-30=15

    • q=523

  • Step 2: Plug into our Specific heat equation

Investigation 8 | Experience 1

Specific heat Sample Problem 3b

• A 85 g piece of Copper Alloy is heated from 30 °C to 45°C. In the process it absorbs 523 J of energy as heat. How much energy will the same sample loose if it is cooled from 45°C to 25°C

  • Step 1: Identify what variables we know

    • c_p=

    • m=

    • Δ​T=

    • q=

    ​

Investigation 8 | Experience 1

Specific heat Sample Problem 3b

• A 85 g piece of Copper Alloy is heated from 30 °C to 45°C. In the process it absorbs 523 J of energy as heat. How much energy will the same sample loose if it is cooled from 45°C to 25°C

  • Step 1: Identify what variables we know

    • c_p=0.41

    • m= 85

    • Δ​T= 25-45=-20

    • q=?

  • Step 2: Plug into our energy equation

Investigation 8 | Experience 1