R1.1 Enthalpy Changes Flashcards
What is the law of conservation of energy?
The total amount of energy in a closed system remains constant; energy can neither be created nor destroyed.
This principle is fundamental in chemistry and is also known as the first law of thermodynamics.
Define energy in the context of chemistry.
Energy is the ability to do work or cause a change, measured in joules (J).
Energy exists in many forms, including kinetic, potential, thermal, and chemical energy.
What are the three main processes for energy transfer?
- Conduction
- Convection
- Radiation
These processes illustrate how thermal energy can be transferred, for example, in a boiling pot of water.
What happens to energy during a chemical reaction?
Energy may change from one form to another, but the total amount of energy remains the same in a closed system.
This transformation can involve heat, light, or sound energy.
What are reactants and products in a chemical reaction?
Reactants are the initial substances, and products are the new substances formed as a result of the chemical reaction.
The rearrangement of atoms occurs during a chemical reaction.
What is the difference between heat and temperature?
Heat is the energy transferred from a region of high temperature to a region of low temperature, while temperature measures the average kinetic energy of particles.
Heat is measured in joules (J), and temperature is measured in Kelvin (K) or degrees Celsius (°C).
Define exothermic reactions.
Exothermic reactions are those that release energy to the surroundings.
Examples include combustion and neutralization reactions.
Define endothermic reactions.
Endothermic reactions are those that absorb energy from the surroundings.
Photosynthesis is a common example of an endothermic reaction.
What effect do exothermic reactions have on temperature?
Exothermic reactions typically cause an increase in the temperature of the surroundings.
This is due to the release of energy in the form of heat.
What effect do endothermic reactions have on temperature?
Endothermic reactions typically cause a decrease in the temperature of the surroundings.
An example is the evaporation of alcohol, which absorbs heat from the skin.
What is chemical potential energy?
Chemical potential energy is the energy stored in the bonds of chemical compounds.
This energy can be transformed during chemical reactions.
Fill in the blank: The chemical equation for the combustion of methane is CH4(g) + 2O2(g) → _______.
[CO2(g) + 2H2O(l)]
What types of energy can be released or absorbed during chemical reactions?
- Heat
- Light
- Electrical energy
Examples include the combustion of wood (heat), luciferin in fireflies (light), and oxidation in batteries (electrical).
Define chemical potential energy.
The energy stored in the chemical bonds between particles.
What does an energy profile diagram represent?
The relative stability of reactants and products based on their chemical potential energy.
In an exothermic reaction, how do the potential energies of products and reactants compare?
Products have lower potential energy than reactants.
In an endothermic reaction, how do the potential energies of products and reactants compare?
Reactants have greater stability due to lower potential energy.
What is biodiesel produced from?
Waste vegetable oil or waste animal fats.
What does standard enthalpy change of reaction refer to?
Heat transferred at constant pressure and under standard conditions.
specific heat capacity of water?
4.18 J g−1 K−1.
thermal energy (heat absorbed or released) equation
Using the equation Q = m × c × ΔT.
What is calorimetry used for?
To measure the heat transfer during a physical or chemical process.
Why is water commonly used in calorimetry?
It has a relatively high heat capacity and is safe for measurement.
What is the density of water?
1.00 g cm−3.
