Unit 10: Energy, Rates, and Equilibrium
A first, mostly qualitative look at the energy a reaction releases or absorbs, what speeds a reaction up, and what it means for a reaction to reach balance.
9 topics · 27 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
10.1 Exothermic and Endothermic Reactions
- How it worksHow does a reaction that releases more energy than it absorbs end up warming its surroundings?
- Common mistakeWhy doesn't an endothermic reaction mean no energy is involved in the reaction at all?
- Going furtherWhat happens to the surrounding temperature when a reaction absorbs more energy than it releases?
Your turn1 of 2
A reaction converts reactants holding 1423 kJ of chemical energy into products holding 1333 kJ of chemical energy. Find delta H for the reaction, in kJ (products minus reactants).10.2 Enthalpy and Reaction Energy Diagrams
- How it worksHow does a reaction energy diagram show the enthalpy difference between reactants and products?
- Common mistakeWhy doesn't the height of the hump in an energy diagram tell you whether a reaction releases or absorbs energy?
- Going furtherWhat happens to a reaction's energy diagram when a catalyst lowers the height of the hump?
Your turn1 of 2
On a reaction energy diagram, the reactants sit at 120 kJ, and the transition-state hump sits at 330 kJ. Find the activation energy for the forward reaction (the hump's energy minus the reactants' energy).10.3 Measuring Heat with a Calorimeter
- How it worksHow does a calorimeter use the temperature change of water to calculate the heat released by a reaction?
- Worked exampleFind the heat released when 100 grams of water rises from 20 to 45 degrees C, using specific heat 4.18 J/(g times degrees C).
- Common mistakeWhy doesn't a calorimeter need to trap every single joule of heat to still give a useful measurement?
Your turn1 of 2
Find the heat released when 351 grams of water rises from 25 to 86 degrees Celsius, using a specific heat of 4.18 J/(g times degrees C) for water.10.4 Specific Heat Capacity
- How it worksHow does a substance's specific heat capacity determine how much its temperature rises for a given amount of heat?
- Worked exampleFind the amount of heat needed to raise the temperature of 50 grams of water from 25 to 75 degrees C.
- Common mistakeWhy doesn't every substance need the same amount of energy to heat up by the same number of degrees?
Your turn1 of 2
Find the amount of heat needed to raise the temperature of 280 grams of water from 29 to 92 degrees Celsius, using water's specific heat of 4.18 J/(g times degrees C).10.5 Factors That Affect Reaction Rate
- How it worksHow do concentration, temperature, and surface area each change how often reacting particles collide?
- Common mistakeWhy doesn't adding more of a reactant always speed up a reaction by the same amount every time?
- Going furtherWhat happens to a reaction's rate when you crush a solid reactant into a fine powder?
Your turn1 of 2
A cloud of fine flour dust suspended in the air can ignite in a violent, explosive burst, while the exact same flour compacted into a solid loaf of bread barely reacts at all when exposed to a spark. Why does a spark ignite a cloud of flour dust far more violently than it ignites a solid loaf of bread?10.6 Collision Theory
- How it worksHow does a collision need both enough energy and the right orientation to actually react?
- Common mistakeWhy doesn't every collision between reactant particles result in a chemical reaction?
- Going furtherWhat happens to the fraction of successful collisions when the temperature of a reaction mixture is raised?
Your turn1 of 2
Reactant particles in a gas or solution collide with each other an enormous number of times every second, yet only a small fraction of those countless collisions actually result in a new product forming. Why do most collisions between reacting particles fail to produce any product at all?10.7 Catalysts and Activation Energy
- How it worksHow does a catalyst lower a reaction's activation energy without being used up itself?
- Common mistakeWhy doesn't a catalyst change the overall energy released or absorbed by a reaction?
- Going furtherWhat happens to a reaction's activation energy barrier when an enzyme acts as a biological catalyst?
Your turn1 of 2
A catalyst lowers a reaction's activation energy from 239 kJ to 65 kJ. Find the reduction in activation energy the catalyst achieves.10.8 Reversible Reactions and Dynamic Equilibrium
- How it worksHow do the forward and reverse reaction rates become equal once a system reaches dynamic equilibrium?
- Common mistakeWhy doesn't equilibrium mean the amounts of reactants and products have become equal to each other?
- Going furtherWhat happens to the concentrations of reactants and products once a reversible reaction reaches equilibrium?
Your turn1 of 2
A reversible reaction that has reached equilibrium shows no further visible change in the concentrations of reactants or products, as if the whole reaction had simply stopped running entirely. Why does a reaction at equilibrium look like it's stopped even though molecules are still reacting?10.9 Le Chatelier's Principle
- How it worksHow does a system at equilibrium shift to partially counteract a change in concentration, pressure, or temperature?
- Worked exampleWalk me through how the equilibrium N2 + 3H2 makes 2NH3 shifts when more nitrogen gas is added.
- Common mistakeWhy doesn't Le Chatelier's principle mean a system fully cancels out the change you made to it?
Your turn1 of 2
Adding extra nitrogen gas to a system already at equilibrium in the reaction N2 + 3H2 makes 2NH3 causes the system to produce more ammonia than it had before, shifting the balance rather than staying exactly where it was. Why does adding more reactant to a system at equilibrium push the reaction to make more product?