Reaktionsweg Faustformel – Calculation example: You travel in your car at 50 km/h. The calculation: (50 km/h: 10) x 3 = 15-meter reaction distance. (50 km/h: 10) x (50 km/h : 10) = 25 meters normal braking distance. The stopping distance is around 40 meters.
The reaction path is the distance you travel before you recognize the danger – and therefore, move your foot from the accelerator to the brake pedal – and start braking.
Humans need about a second to react to danger. During this time, your car will continue to drive without braking.
Using this rule of thumb a reaction path can remain easily calculated
You drive your car at 50 km/h: 10 = 5 x 3 = 15
According to this, your car travels 15 meters per second until you, recognizing the danger, put your foot on the accelerator and apply it to the brake.
If you drive at 100 km/h, for example, on the motorway, it is 30 m per second before you even brake.
If you drive at 30 km/h, it’s still a whopping 9 m per second, for example, in a 30 zone where children play or in schools.
The braking distance is between the start of braking and the vehicle coming to a standstill.
It Calculates How Many Meters The Car Travels When Braking. Calculation Example:
- You drive your car 50 km/h 50 km/h: 10 = 5 x 50 km/h: 10 = 5 = 25 meters
- If you drive 100 km/h: 100 km/h: 10 = 10 x 100 km/h: 10 = 10 = 100 meters
- If you drive 30 km/h: 30 km/h: 10 = 3 x 30 km/h: 10 = 3 = 9 meters
The braking distance consists of the calculation of the reaction distance + the calculation of the braking distance.
Calculation Example, We Remember:
to the formula for the reaction distance + the calculation for the braking distance = together you get your braking distance
The most important rule of thumb you need for the theory test is summarized again for you.
Recognize – decide – react
For us humans, we assume a reaction time of around one second.
Reaction path in m
Response time 2 seconds
From the start of braking until the vehicle comes to a standstill.
Braking distance in m
Recognizing the danger until the vehicle comes to a standstill.
Stopping distance in m = reaction distance in m + braking distance in m
Braking distance during emergency braking:
The Influence Of Temperature On Reaction Rates
In practice, rate constants vary in response to changes in various factors. They are usually the same in two experiments only if everything is identical except for the reagent concentrations. In other words, the rate law captures the dependence of the reaction rate on concentrations. In contrast, the dependence of the reaction rate on any other variable appears as the dependence of the rate constant on that variable.
Temperature usually has a big influence. The experimentally observed dependence of the rate constants on temperature can remain expressed compactly. For small temperature ranges, it can usually remain adequately expressed by the Arrhenius equation:
are called the Arrhenius activation energy or frequency factor (or pre-exponential factor).
The Arrhenius equation is an empirical relationship. As we see below for our collision theory model, theoretical treatments predict that the pre-exponential term A is weakly temperature-dependent. When we study reaction rates experimentally, the temperature dependence of A remains usually obscured by the uncertainties in the measured rate constants. As a rough rule of thumb, it remains often said that a chemical reaction’s speed doubles when the temperature increases by 10 K. However, this rule can fail spectacularly. A reaction may proceed more slowly at higher temperatures, and there are multistep reactions in which this remains observed.
This page, titled 5.4: The Effect of Temperature on Reaction Rates, is shared under a CC BY-SA 4.0 license and is written, remixed, and curated by Paul Ellgen from source content in the style and standards of the LibreTexts platform edited detailed processing history is available upon request.
As a rule of thumb, the reaction rate of many reactions doubles for every ten-degree Celsius increase in temperature. For a given reaction, the ratio of its rate constant at a higher temperature to its rate constant at a lower temperature is called the temperature coefficient (Q).