4.5 Energy changes Flashcards
(18 cards)
What is enthalpy change?
Enthalpy change (ΔH) is the heat energy change during a reaction at constant pressure.
What are exothermic reactions?
Exothermic reactions release energy to the surroundings, resulting in an increase in temperature (e.g., combustion, respiration).
What are endothermic reactions?
Endothermic reactions absorb energy from the surroundings, resulting in a decrease in temperature (e.g., thermal decomposition).
What is activation energy?
Activation energy is the minimum energy required for a reaction to take place.
What is the equation for calculating energy change using bond energies?
ΔH = (Total bond energy of bonds broken) - (Total bond energy of bonds formed).
What happens in an exothermic reaction?
In an exothermic reaction, energy is released when new bonds are formed, and the energy of the products is lower than the energy of the reactants.
What happens in an endothermic reaction?
In an endothermic reaction, energy is absorbed to break bonds, and the energy of the products is higher than the energy of the reactants.
What is bond energy?
Bond energy is the energy required to break one mole of a particular bond in a molecule in the gaseous state.
What is an energy profile diagram?
An energy profile diagram shows the change in energy during a reaction. Exothermic reactions show a downward slope and endothermic reactions show an upward slope.
What is a catalyst?
A catalyst is a substance that speeds up a chemical reaction without being consumed by lowering the activation energy.
How does a catalyst work?
A catalyst provides an alternative reaction pathway with a lower activation energy allowing the reaction to occur more quickly.
What is the significance of activation energy in reactions?
Activation energy determines how easily a reaction will occur. Higher activation energy means a slower reaction and lower activation energy means a faster reaction.
What is the purpose of calorimetry?
Calorimetry measures the amount of heat energy released or absorbed during a chemical reaction typically using water as the heat sink.
What is the formula for calculating the energy change in a reaction using bond energies?
Energy change = Total bond energy of bonds broken - Total bond energy of bonds formed.
What is the calculation for heat energy change using temperature change?
Q = mass x specific heat capacity x temperature change (Q is the heat energy in joules).
What is specific heat capacity?
Specific heat capacity is the amount of energy needed to raise the temperature of 1 gram of a substance by 1°C.
What is an example of an exothermic reaction?
Combustion of methane (CH₄) or wood.
What is an example of an endothermic reaction?
Thermal decomposition of calcium carbonate (CaCO₃) to calcium oxide (CaO) and carbon dioxide (CO₂).
