1 / 13

Energy

Thermochemistry: The study of heat changes that occur during chemical reactions and physical changes of state. Energy. Energy – the ability to do work or produce heat Heat (q) = the energy that transfers from one object to another because of a temperature difference between them

thane-robbins
Download Presentation

Energy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

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 • 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 • Potential energy – in a chemical reaction deals with the types of atoms & what bonds they form

  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 = 4.186 J

  6. 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)

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

  8. 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.

  9. Example • C= q/ (m∆T) • C=114 J/ (10.0 g x 25.4°C) • c = 0.449 J/g C

  10. 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

  11. 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 – 25.0°C) • q = 4520 J

  12. 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

  13. 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 = 475C • T = Tf-Ti • 475 = Tf - 25 • Tf = 500 C

More Related