Energy Change & Rates of RXN NOTES
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90 Terms
What is defined as the net change of chemical potential energy of the system?
Heat of reaction (∆H)
What type of reaction transforms chemical potential energy into thermal energy?
Exothermic reactions
What type of reaction transforms thermal energy into chemical potential energy?
Endothermic reactions
What is the relationship between bond strength and energy required to break bonds?
A stronger bond requires more energy to break.
What is the predicted value of (∆H) for endothermic reactions?
(∆H) > 0
What is the predicted value of (∆H) for exothermic reactions?
(∆H) < 0
What is activation energy?
The minimum energy required to start a chemical reaction.
What is the activated complex?
A high energy, unstable, temporary transition state between reactants and products.
How is reaction rate defined?
The change in concentration per unit time of either a reactant or product.
What factors affect the rate of chemical reactions?
Nature of reacting substances, surface area, concentration, pressure, temperature, and catalysts.
What is a catalyst?
A substance that increases the rate of the reaction but remains unchanged at the end.
What does collision theory explain?
A reaction will only proceed when reactant particles collide effectively.
What is the effect of temperature on reaction rates according to collision theory?
Higher temperatures increase the number of effective collisions.
What is an endothermic process?
An endothermic process is one in which the system absorbs heat from its surroundings.
What does 'exo-' mean in the context of reactions?
'Exo-' means 'out of' in relation to energy transfer in exothermic reactions.
What happens to the surroundings during an exothermic process?
The surroundings gain heat, causing their temperature to rise.
How is energy transfer indicated in exothermic and endothermic processes?
Exothermic processes are given a negative sign (-) and endothermic processes a positive sign (+).
What is the effect of an endothermic process on the surroundings?
The temperature of the surroundings decreases as the system absorbs heat.
What happens to bonds during a chemical reaction?
Bonds in the reactants break while new bonds form in the products.
What is bond energy?
Bond energy is the energy required to break a bond or released when a bond is formed.
Define an exothermic reaction.
An exothermic reaction is one where more energy is released when forming bonds than is absorbed for breaking bonds.
What is (∆H) in an exothermic reaction?
(∆H) is less than zero.
Define an endothermic reaction.
An endothermic reaction is one that absorbs energy from the surroundings.
What is (∆H) in an endothermic reaction?
(∆H) is greater than zero.
What is activation energy (EA)?
Activation energy is the minimum kinetic energy required to start a chemical reaction.
What is the activated complex?
The activated complex is a high energy, unstable transition state between reactants and products.
What is reaction kinetics?
The study of how fast a reaction takes place and the macroscopic conditions affecting the reaction rate.
What is required for two molecules to react chemically?
They must come into contact with sufficient kinetic energy to overcome existing bonds and have the correct orientation.
What does collision theory state?
The rate of a reaction depends on the number of effective collisions occurring per second between reacting molecules.
How is reaction rate defined?
As the change in concentration per unit time of either a reactant or product.
What happens to reactants in a faster reaction?
Reactants are used up quickly, and products are formed quickly.
What is the relationship between reaction rate and concentration of reactants?
Higher concentrations typically lead to a higher reaction rate due to increased frequency of effective collisions.
What does a steep gradient in a reaction rate graph indicate?
The fastest reaction rate, as it shows a high volume of product formation over time.
What does the gradient of the tangent to a curve represent in reaction kinetics?
The instantaneous reaction rate.
How is the average reaction rate calculated?
By measuring the change in concentration over a specified time interval.
What is the effect of time on the instantaneous reaction rate?
The instantaneous reaction rate decreases with time as reactants are consumed.
How can the rate of a reaction be measured?
The rate of a reaction can be measured by determining the amount of reactant used per time or the amount of product produced per time.
What are common methods to measure reaction rates?
Common methods include measuring changes in color, gas collected per unit time, or the amount of precipitate formed.
What method is suitable for measuring gas production in a reaction?
The suitable method is to collect the gas in a gas syringe and measure the amount collected at various times.
What is another method to measure gas production in a reaction?
Another method is the downward displacement of water, where gas displaces water in an inverted measuring cylinder.
How can the rate of a reaction be measured?
By determining the amount of reactant used per time or the amount of product produced per time.
What is a common method to measure gas production in reactions?
Collecting gas in a gas syringe or using downward displacement of water.
What happens to the gas syringe during the reaction of calcium carbonate with hydrochloric acid?
The plunger is pushed out as carbon dioxide is produced.
What determines the maximum amount of carbon dioxide produced in the reaction?
The amount of calcium carbonate and hydrochloric acid available.
What measurement indicates a change in mass during a reaction?
The mass of carbon dioxide produced.
How can the mass change be measured in a reaction?
By measuring the mass of the reactants over time.
What apparatus can be used to collect gas during a reaction?
An inverted graduated cylinder filled with water.
What role does cotton wool play in the reaction setup?
It allows gas to escape while preventing liquid from escaping.
What is the importance of not sealing the reaction vessel when measuring mass changes?
Sealing would prevent gas escape, leading to inaccurate mass measurements.
What is turbidity in the context of chemical reactions?
Turbidity refers to the cloudiness or haziness of a solution, often due to precipitate formation during a reaction.
What is formed when sodium thiosulfate reacts with an acid?
A yellow precipitate of sulfur is formed.
How can the average rate of the reaction between sodium thiosulfate and acid be estimated?
By measuring the time taken for a black cross beneath the flask to disappear due to precipitate formation.
What instrument can be used to measure the light transmitted through a sample during the reaction?
A light meter or spectrophotometer.
What indicates a change in colour during a reaction?
The presence of an indicator or the production of transition metal salts.
How can the intensity of a colour change be measured?
Using a light meter.
What factors determine the rate of a chemical reaction?
The nature of the reactants and the conditions of the reaction.
What are the two types of reactions based on heat exchange?
Exothermic and Endothermic reactions
What factors affect the rate of a chemical reaction?
Surface area, concentration, pressure, temperature, and catalyst.
What is the effect of increasing the concentration of hydrochloric acid on the reaction with calcium carbonate?
It increases the rate of reaction.
What is the role of a catalyst in a chemical reaction?
A catalyst speeds up the reaction without being consumed.
What is the effect of temperature on the reaction rate?
Increasing the temperature generally increases the rate of reaction.
What is produced when zinc reacts with hydrochloric acid?
Hydrogen gas and zinc chloride.
What is the impact of using a copper catalyst in the reaction between zinc and hydrochloric acid?
It increases the rate of hydrogen gas production.
How does increasing the surface area of a solid affect the rate of reaction?
It increases the rate of reaction.
What is the effect of concentration on the rate of chemical reactions?
Increasing concentration increases the rate of reaction.
How does pressure affect the rate of reaction in gases?
Increasing pressure increases the rate of reaction.
What happens to the rate of reaction when temperature is increased?
The rate of reaction increases.
What is the relationship between temperature and activation energy in reactions?
Higher temperature increases the proportion of particles with kinetic energy greater than activation energy.
What does collision theory state about the effect of surface area on reaction rates?
More surface area leads to more collisions and effective collisions.
Why does the rate of reaction decrease over time?
The concentration of reactants decreases.
How does an increase in temperature affect reaction rates?
An increase in temperature leads to more reactant particles having kinetic energy greater than the activation energy, resulting in more collisions per unit time.
What is the effect of a catalyst on reaction rates?
A catalyst increases the rate of reaction by providing an alternative path with lower activation energy.
Define a catalyst.
A catalyst is a substance that increases the rate of a reaction but remains unchanged at the end of the reaction.
What is the role of activation energy in chemical reactions?
Activation energy is the minimum energy required for reactant particles to collide and react.
According to collision theory, how does a catalyst affect effective collisions?
A catalyst provides an alternative path for the reaction with lower activation energy, leading to a greater frequency of effective collisions.
What does the Maxwell-Boltzmann distribution graph illustrate?
The Maxwell-Boltzmann distribution graph illustrates the distribution of kinetic energy among particles in a system.
What happens to the activation energy when a catalyst is added?
The activation energy is lowered when a catalyst is added.
What is an activated complex?
An activated complex is a temporary, unstable arrangement of atoms that occurs during the transition from reactants to products.
Is the breaking of bonds an endothermic or exothermic process?
Endothermic process
What is the reaction for the Haber process?
N₂(g) + 3H₂(g) → 2NH₃(g)
How do you determine if a reaction is endothermic or exothermic?
By analyzing the sign of (∆H)
What is activation energy?
The minimum energy required for a reaction to occur.
How can a catalyst affect the (∆H) value for a reaction?
A catalyst does not change the (∆H) value.
How does the concentration of hydrochloric acid affect the rate of reaction with calcium carbonate?
Higher concentration increases the rate of reaction.
What experimental technique can be used to determine the rate of reaction related to a product?
Gas collection method
What effect does increasing the surface area of zinc have on the rate of reaction with hydrochloric acid?
Increases the rate of reaction.
What is the expected graph shape for the volume of hydrogen gas produced over time when zinc reacts with sulfuric acid?
The graph will show a rapid increase in volume that levels off as the reaction completes.
What is the effect of using powdered zinc instead of zinc pieces on the rate of reaction with hydrochloric acid?
The reaction rate will increase.
How does using a catalyst affect the average rate of a chemical reaction?
It increases the rate of reaction.
What are four factors that increase the rate of a chemical reaction?
Temperature
Concentration
Surface area
Presence of a catalyst