Lesson: Thermochemistry

​Here are the important things from the video:

• Thermochemistry- branch of chemistry that deals with the heat exchange in a chemical process

​Here are the important things from the video:

• Chemical process can exothermic or endothermic

  • exothermic- releases energy during the chemical process. feels hot to the touch, gets hotter

  • endothermic- absorbs energy during chemical process. feels cold to the touch, gets colder

​Here are the important things from the video:

• Enthalpy (ΔH)- represents the change in enenrgy of a reaction

  • positive ΔH (+ΔH)

    • energy in products > energy in reactants.

    • endothermic process

  • negative ΔH (-ΔH)

    • energy in products < energy in reactants

    • exothermic process

​Some important distinction:

• Energy- the capacity to work

• heat (q)- energy tht flow between a system and its surrounding

  • system- substance we are focused on

  • surrounding- the space around the system

  • heat flow

    • always from High energy (hot) to low enenrgy (cold)

  • +q endothermic

  • -q exothermic

  • q is like ΔH

​​Some important distinction:

Temperature- measurement of the average kinetic energy (energy) of a substance

​Unit of Heat

Joules (J) and kJ (kilojoules)

• 1000 J = 1 kJ

Calories (cal) and kcal (kcal)

• 1000 cal = 1 kcal =1 Cal

1 calorie = 4.184 J

​Thermochemical Equation

• a balanced chemical equation showing the amount of heat change for a reaction.

• Can be seen in these 2 ways

​The euqation above tells us the mole ratio so we can use this to solve stiochiometry for any value.

Open Ended

What is thermochemistry?

Multiple Choice

In an exothermic reaction, heat is ...

• taken in

• given out

Multiple Choice

In an endothermic reaction, heat is ...

• taken in

• given out

Multiple Choice

Using the thermochemical eq. given, calculate the heat evolved when 266 g of white phosphorus burns in air.

• -6.47 x 10^3 kJ

• -6468 kJ

• 6.47 x 10^3 kJ

• 6468 kJ

​Using the thermochemical eq. given, calculate the heat evolved when 266 g of white phosphorus (P₄) burns in air.

P₄ + 5O₂ → P₄O₁₀ ΔH=-3013 kJ

​Plan:

Given: 266 g P₄

Want: heat evolved in kJ

g P₄→mol P₄→kJ

Multiple Choice

Given the thermochemical equation, calculate the heat evolved when 74.6 g of sulfur dioxide (molar mass = 64.07 g/mol) is converted to sulfur dioxide.

• -115 kJ

• 115 kJ

• -115.39 kJ

• 115.39 kJ