Half Life 2 is a first-person shooter by Valve Corporation. Six years did fans of the critically acclaimed Half Life have to wait for its successor, Half Life 2. Developed by the Valve Corporation, it was the very first game to use the developer's Source engine. Continuing the story of scientist-turned-action-hero Gordan Freeman in a alternate. A medication's biological half-life refers simply to how long it takes for half of the dose to be metabolized and eliminated from the bloodstream. Or, put another way, the half-life of a drug is the time it takes for it to be reduced by half. For example, the half-life of ibuprofen (the active ingredient in pain and fever relievers such as. Half-Life: Alyx. The latest entry in the Half-Life series, Half-Life: Alyx is a virtual reality video game developed by Valve. It was announced on November 18th, 2019, and released on March 23rd, 2020 for Microsoft Windows and May 15th, 2020 for Linux. Set five years before the events of Half-Life 2, the game follows a 19-year-old Alyx Vance as. Half-life definition, the time required for one half the atoms of a given amount of a radioactive substance to disintegrate.
Half Lives
We use integrated rate laws, and rate constants to relate concentrations and time. The rate law to use depends on the overall order of the reaction.
Equations for Half Lives
For a zero order reactionA products , rate = k:
t½ = [Ao] / 2kFor a first order reaction A products , rate = k[A]:
t½ = 0.693 / kFor a second order reaction 2A products or A + B products (when [A] = [B]), rate = k[A]2:
t½ = 1 / k [Ao]
Determining a Half Life
To determine a half life, t½, the time required for the initial concentration of a reactant to be reduced to one-half its initial value, we need to know:
- The order of the reaction or enough information to determine it.
- The rate constant, k, for the reaction or enough information to determine it.
- In some cases, we need to know the initial concentration, [Ao]
Substitute this information into the equation for the half life of a reaction with this order and solve for t½. The equations are given above.
Converting a Half Life to a Rate Constant
To convert a half life to a rate constant we need to know:
- The half life of the reaction, t½.
- The order of the reaction or enough information to determine it.
- In some cases, we need to know the initial concentration, [Ao]
Substitute this information into the equation for the half life of a reaction with this order and solve for k. The equations are given above.
Graphical Relations and Half Lives
If we plot the concentration of a reactant versus time, we can see the differences in half lives for reactions of different orders in the graphs. We can identify a 0, 1st, or 2nd order reaction from a plot of [A] versus t by the variation in the time it takes the concentration of a reactant to change by half.
For a zero order reactionA products , rate = k:
For a first order reaction A products , rate = k[A]:
For a second order reaction 2A products or A + B products (when [A] = [B]), rate = k[A]2:
The following tools can generate any one of the values from the other three in the half-life formula for a substance undergoing decay to decrease by half.
Half-Life Calculator
Half-life Formula
Please provide any three of the following to calculate the fourth value.
Half-Life, Mean Lifetime, and Decay Constant Conversion
Please provide any one of the following to get the other two.
Definition and Formula
Half-life Formula
Half-life is defined as the amount of time it takes a given quantity to decrease to half of its initial value. The term is most commonly used in relation to atoms undergoing radioactive decay, but can be used to describe other types of decay, whether exponential or not. One of the most well-known applications of half-life is carbon-14 dating. The half-life of carbon-14 is approximately 5,730 years, and it can be reliably used to measure dates up to around 50,000 years ago. The process of carbon-14 dating was developed by William Libby, and is based on the fact that carbon-14 is constantly being made in the atmosphere. It is incorporated into plants through photosynthesis, and then into animals when they consume plants. The carbon-14 undergoes radioactive decay once the plant or animal dies, and measuring the amount of carbon-14 in a sample conveys information about when the plant or animal died.
Below are shown three equivalent formulas describing exponential decay:
- where
N0 is the initial quantity
Nt is the remaining quantity after time, t
t1/2 is the half-life
τ is the mean lifetime
λ is the decay constant
If an archaeologist found a fossil sample that contained 25% carbon-14 in comparison to a living sample, the time of the fossil sample's death could be determined by rearranging equation 1, since Nt, N0, and t1/2 are known.
Half Life Of Caffeine
This means that the fossil is 11,460 years old.
Derivation of the Relationship Between Half-Life Constants
Half-life Equation
Using the above equations, it is also possible for a relationship to be derived between t1/2, τ, and λ. This relationship enables the determination of all values, as long as at least one is known.