Presentation is loading. Please wait.

Presentation is loading. Please wait.

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

Similar presentations


Presentation on theme: "Thermochemistry: The study of heat changes that occur during chemical reactions and physical changes of state."— Presentation transcript:

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

2 Energy Energy – the ability to do work or produce heat
Exists in 2 forms: Kinetic energy – energy of motion Potential energy – energy at rest or energy of position Heat (q) = the energy that transfers from one object to another because of a temperature difference between them Heat always flows from a warmer object to a cooler object

3 Energy Kinetic energy – in a chemical reaction temperature is the determining factor The higher the temperature…the faster the particles move…the higher the average kinetic energy Temperature is a measure of the average kinetic energy Kelvin scale: 0 K = -273 °C

4 Law of Conservation of Energy
Law of Conservation of Energy – Energy is neither created nor destroyed

5 Heat (q) Heat or energy can be in joules, calories, kilocalories, or kilojoules The SI unit is the joule 1 Cal = 1000 cal = 1 kcal 1 cal = J 1kcal = 4186J 1 J = cal

6 Heat Capacity The amount of heat it takes to change an object’s temperature by 1ºC Depends on an object’s mass Ex. A cup of water has a greater heat capacity than a drop of water.

7 Specific Heat (C) Specific Heat (C) – the amount of heat required to raise 1 gram of a substance by 1C Specific heat is an intensive property, and therefore does not depend on size Every substance has its own specific heat Ex. Water = 4.18 J/(g x ºC) Glass = 0.50 J/(g x ºC)

8 Specific Heat Units for C = J / (g x ºC) (joules per gram degree Celsius) Equation for Specific Heat: C = q / (m Δ T) C = specific heat; q = heat; m = mass and ΔT = change in temperature This equation can be rearranged to solve for heat (q) q= CmΔT

9 Specific Heat A 10.0 g sample of iron changes temperature from 25.0C to 50.4 C while releasing 114 joules of heat. Calculate the specific heat of iron.

10 Example C= q/ (m∆T) C=114 J/ (10.0 g x 25.4°C) C = 0.45 J/g C

11 Another example If the temperature of 34.4 g of ethanol increases from 25.0 C to 78.8 C how much heat will be absorbed if the specific heat of the ethanol is 2.44 J/g C

12 Another example First, rearrange the specific heat formula to solve for heat q = CmT q = (2.44 J/g°C)(34.4g)(78.8°C - 25°C) q = J

13 Yet another example 4.50 g of a gold nugget absorbs 276 J of heat. What is the final temperature of the gold if the initial temperature was 25.0 C & the specific heat of the gold is 0.129J/g C

14 Yet another example C= q/ (m∆T); rearrange to find ∆T = q / (C x m)
∆T = 276 J / (.129 J/g°C x 4.50 g) T = C T = Tf-Ti = Tf-25 Tf = C


Download ppt "Thermochemistry: The study of heat changes that occur during chemical reactions and physical changes of state."

Similar presentations


Ads by Google