Enegertics and thermodynamics Flashcards
Why is energy required in chemical reaction?
All chemical reactions involve energy. Energy is needed to break bonds in reactants. These bonds may be very strong.
When is energy given out in chemical reaction?
Energy is released when new bonds form in the products. That’s because the atoms now have a more stable arrangement of electrons.
What is the most important type of energy in chemistry?
Heat.
What is the exothermic reaction?
When heat is given out to the surroundings.
What is the endothermic reaction?
When heat is absorbed from the surroundings.
What is enthalpy (H)?
The inside energy of any matter is called Enthalpy.
Is it possible to know the absolute value of the enthalpy of the reactants or of the products? What is can really be measured in enthalpy?
The absolute value of Enthalpy (H) is not possible to measure. Only the difference of Enthalpy (𝛥H) is possible to measure.
When is ΔH negative and when is it positive?
- Its negative during exothermic reaction.
- Its positive during endothermic reaction.
What is the difference between heat and temperature?
Heat is a measure of the total energy in a given amount of substance. While temperature is a measure of the hotness of a substance. Heat depends on the amount of substance present. Temperature represents the average kinetic energy of a substance and does not depend on the amount of substance present.
How to make a calculation for ΔH?
Step: 1. Write equation for reaction.
Step 2: Calculate molar quantities.
Step 3: Calculate heat evolved.
How to calculate heat energy?
E= cmΔT
What is the unit for ΔH?
KJ/ mol
What is Hess´ Law? Is this law a statement of another law? What is the use of Hess´ Law. Show this in an example.
Enthalpy change for a reaction depends only on the difference between the enthalpy of the products and the enthalpy of the reactants.
The enthalpy change going from A to B is the same whether the reaction proceeds directly to A or whether t goes via an intermediate.
Statement of the law of conservation of energy. It can be used to determine enthalpy changes, which cannot be measured directly. For example, the enthalpy of combustion of both carbon and carbon monoxide to form carbon dioxide can easily be measured directly, but the combustion of carbon to carbon monoxide cannot.
What is entropy?
The disorder of a system is known as Entropy.
When is ΔS negative?
Systems which become more ordered.
