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### Course: Class 11 Biology (India)>Unit 8

Lesson 7: Enzymes

# Introduction to kinetics

Kinetics is the study of reaction rates and how they are affected. Many factors, such as concentration, pressure, temperature, and enzyme activity, can impact the rate of a reaction. For example, a molecule's kinetic energy is directly proportional to its temperature, so increasing the temperature will result in an increase in reaction rate. Created by Sal Khan.

## Want to join the conversation?

• Doesn't pressure also increase the reaction rate??
• Yes, if it is a reaction between gases. If you increase the partial pressure of each reactant, you will increase the collision rate between molecules, since you will be increasing the gas activity, but it only works for gaseous reactions !
However, you have to be careful by using this information, because if you analyze a reaction between two aquous reactants, depending on the circumstances there can be an equilibrium between liquid and gasous states of a reactant, so increasing its the vapour pressure might increase its aquous concentration and then affect the reaction rate. Its most of the time related to the concentration and molecules quadratic speeds.
• Can someone explain this in baby words because I only understand half of it?
• Kinetics is like a superhero that helps us understand how fast or slow things happen in the world of chemistry and physics. It's all about the speed of reactions and how things change.

Imagine you have a bowl of ice cream on a hot day. What happens to the ice cream? It melts, right? Kinetics helps us understand how fast the ice cream melts. It's like asking, "How quickly does the ice cream turn from solid to liquid?"

There are two main things we look at in kinetics: reaction rates and factors that affect them.

Reaction Rates: Reaction rates tell us how fast a reaction is happening. Think of it as measuring the speed of a car. Some reactions happen really quickly, like a race car zooming by, while others are slow, like a snail crawling. Kinetics helps us measure and understand these different speeds.

Factors Affecting Reaction Rates: Just like a car's speed can be affected by different things like the road condition or the driver, reaction rates can be influenced by various factors too. Some of these factors include temperature, concentration of the reactants (ingredients), and the presence of catalysts (helpers that speed up reactions).

So, kinetics helps us study how fast things change and what factors make them change faster or slower. It's like a detective that helps us figure out the "how" and "why" behind chemical and physical changes.

And that's an introduction to kinetics in baby words! It's all about understanding the speed of reactions and what makes them go fast or slow.
• Is it fair to think about this in terms of velocities of molecules? So if you add heat to the system (increase the velocities of the molecules), then molecules of H2 and I2 will collide at higher velocities (higher energies). My question is: How do all the speeds of the particles change from before reaction, during reaction, and after reaction? Which is moving faster: a H2, I2, or HI after the reaction?
• The average kinetic energies of the molecules are all the same at the same temperature. That means that, if the temperature stays constant, the molecules with less mass must move more rapidly than those with more mass in order to have the same kinetic energy. Thus the H2 molecules are moving faster on average than are the other molecules.
• How do we know whether H2+I2 has more energy than 2HI?
• Can someone define enthalpy please?
• That's very accurately said Noah, great! You definitely understand delta H.

Enthalpy is the total heat contained in a system according to the IUPAC (International Union of Pure and Applied Chemistry which is basically the over watchers of chemistry). Enthalpy can decrease and increase which is represented by a positive (+) or negative (-) sign, with a positive for gaining energy, usually shown in temperature (endothermic or endo). If the reaction is losing energy, it usually is expressed with a negative (I've only known one exception, and i believe it was mathematical error). Negative can be seen in dropping temperatures and is known as being a Exothermic, or exo reaction.

When i refer to temperature, I do not mean only temperature. Enthalpy is a measure of heat, not temperature :) which refers to the energy of the reaction. Reactions use energy to melt, be solidified, or "produce" light.

Hopes this helps!
-Maya
• how is this biology?
• A lot that goes on in biology depends on the chemistry involved. Biological metabolism is almost completely defined in biochemistry.
• At , why does the crushed salt have a larger surface area compared to its original state before it was crushed?
• Try a thought experiment.

What has more surface area: a cube, or the two pieces of a cube cut in half?
• This video assumes a lot of chemistry knowledge, and most biology students haven't taken chemistry yet. They don't know what valence electrons are, what a mole is, etc.